Humidity in the Data Center: Do We Still Need to Sweat It?

Temperature is the hottest topic (pardon the pun) when it comes to maintaining the proper environmental conditions in a data center—particularly in the context of energy consumption and cost—but humidity is also important. But with ASHRAE’s recently expanded allowable and recommended ranges for temperature and humidity, is water vapor still a concern?

Humidity: What You Can’t See Can Hurt Your Data Center

Liquid water is generally a bad thing in your data center, but in the air, it’s something you need in the right proportions. Too much humidity can lead to condensation, which can in turn cause corrosion or—in sufficient amounts—electrical shorts. But too little humidity promotes buildup of electrostatic charge, and discharges of static electricity can damage or destroy sensitive electronics.

Part of the solution is data center measurement and monitoring. Installing humidity sensors (along with temperature sensors) provides information that enables maintaining proper environmental conditions. That’s clear enough. What’s not so clear is what exactly you should measure. Traditionally, relative humidity (RH) has been the metric of choice, with 45% to 55% RH being the espoused ideal range. But inherent difficulties with RH mean it is being used less frequently as a metric. Furthermore, the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) recently expanded its recommended and allowable temperature ranges—as well as its humidity ranges. Given, then, that the traditional view of maintaining 45% to 55% RH in the data center seems to be in flux, what’s the best approach?

Measuring Humidity: Absolute or Relative?

The difficulty with attempting to maintain a relative humidity in the data center is that RH is dependent on temperature: it is a measure of the percentage of water vapor content that air can hold at a given temperature. But because warmer air holds more water, an RH of, say, 50% at 65°F would be significantly lower than 50% at 80°F. The difficulty in the context of data centers is that these facilities deal with both warm air and cool air, which are ideally kept as separate as possible. Cool air flows into a server inlet, is heated and then is ejected as warm exhaust. The water content of this air hasn’t changed during this process (barring, of course, condensation), but the relative humidity of the exhaust is lower than that of the cool air at the server inlet.

An alternative to relative humidity is absolute humidity, which can be expressed as, for instance, the mass of water per mass of dry air. A more familiar measure of absolute humidity is the dew point: the temperature at which water in the air begins condensing (or the temperature at which the RH is 100% for a given air mass). The advantage of measuring and monitoring dew point temperatures instead of relative humidity is that the dew point at the server inlet is the same as that at the server exhaust outlet. A sensor can thus be placed at the server inlet (or the outlet) without the need to worry about getting a humidity measurement at the outlet as well.

Naturally, then, measuring absolute humidity enables companies to have less of a “moving target” with regard to maintaining a specific humidity in their data centers. Furthermore, the recently updated ASHRAE temperature and humidity ranges show a clear recognition of absolute humidity as being important—not just relative humidity.

Expanded ASHRAE Guidelines

A recent whitepaper from The Green Grid discusses the new ASHRAE recommended and allowable ranges in the context of free cooling. Over the recommended temperature range (18°C to 27°C, or about 64°F to 81°F), a portion (temperatures below about 23°C or about 73°F) has a corresponding maximum humidity of 50% (RH). The other portion has a maximum absolute humidity of about 0.011 (measured in grams of water per grams of dry air). The previous (2004) ASHRAE recommended range maintained the traditional RH values of 40% to 55%.

Interestingly, however, the new ASHRAE guidelines still maintain the same overall humidity range—although the recommended humidity varies to some extent with temperature, the absolute humidity should never fall below about 0.006 (same units as above), nor should it ever exceed 0.011. For certain allowable ASHRAE ranges (which should only be used when the data center’s IT equipment can withstand them), the absolute and relative humidity can go beyond the recommended range. Not only do these expanded guidelines give data center operators more leeway with their cooling infrastructure, they also enable more use of free cooling (air-side or water-side economization)—in many areas of the world, throughout the entire year.

Should You Worry About Humidity?

The wider ASHRAE guidelines mean that facilities do not need to sweat humidity as much as they did when 40% to 55% RH was the rule. Furthermore, a growing recognition of absolute humidity (such as dew point) as a better metric means less measurement variation from one side the server (the inlet) to the other (the exhaust outlet). Of course, humidity is still a concern: too much or too little can still cause problems for your IT equipment.

Maintaining a certain humidity range when using mechanical cooling methods often requires addition of (or removal of) water from the air, but this generally involves a fairly closed system. When free cooling is used extensively, the natural variations in temperature and humidity of outside air can complicate the situation, simply by making humidifiers work harder, for instance. Just “opening the windows” of your facility sounds like a great cooling option (it’s certainly cheap), but doing so on particularly rainy or dry days can wreak havoc on your equipment, unless you take steps to regulate water content in the air.

Conclusions

So, should you still sweat humidity in the data center? In some sense, yes: too much or too little water vapor in the air is problematic—nothing about that situation has changed. But as the expanded ASHRAE recommended and allowable operating ranges indicate, many companies and manufacturers are recognizing that the old, tight limits on temperature and humidity are not as necessary as once thought. Thus, although maintaining proper humidity is still critical, it’s not as difficult as it once was (thought to be).

Perhaps the more important industry trend to note is the shift from relative humidity toward absolute humidity as the superior metric. Absolute humidity is just that—absolute, in the sense that it is a measurement of the actual water content of air. Relative humidity measures the percent capacity of air at a given temperature, which can be problematic, because data centers deal with cool air and warm air simultaneously. The current challenge for most facilities is selecting the right temperature and humidity range—whether the recommended range or an allowable range—to maximize the potential for free cooling while still adequately protecting equipment from heat and condensation. So—stay cool and dry, but keep an eye on your energy usage while you’re at it.

Recommended Computer Room Temperature
Operating expensive IT computer equipment for extended periods of time at high temperatures greatly reduces reliability, longevity of components and will likely cause unplanned downtime. Maintaining an ambient temperature range of 68° to 75°F (20° to 24°C) is optimal for system reliability. This temperature range provides a safe buffer for equipment to operate in the event of air conditioning or HVAC equipment failure while making it easier to maintain a safe relative humidity level.
It is a generally agreed upon standard in the computer industry that expensive IT equipment should not be operated in a computer room or data center where the ambient room temperature has exceeded 85°F (30°C).
In today’s high-density data centers and computer rooms, measuring the ambient room temperature is often not enough. The temperature of the air where it enters the server can be measurably higher than the ambient room temperature, depending on the layout of the data center and a higher concentration of heat producing equipment such as blade servers. Measuring the temperature of the aisles in the data center at multiple height levels can give an early indication of a potential temperature problem. For consistent and reliable temperature monitoring, place a temperature sensor at least every 25 feet in each aisle with sensors placed closer together if high temperature equipment like blade servers are in use. We recommend installing Tem PageR, Room Alert 7E or Room Alert 11E rack units at the top of each rack in the data center. As the heat generated by the components in the rack rises, TemPageR and Room Alert units will provide an early warning and notify staff for temperature issues before critical systems, servers or network equipment is damaged.
Recommended Computer Room Humidity
Relative humidity (RH) is defined as the amount of moisture in the air at a given temperature in relation to the maximum amount of moisture the air could hold at the same temperature. In a data center or computer room, maintaining ambient relative humidity levels between 45% and 55% is recommended for optimal performance and reliability.
When relative humidity levels are too high, water condensation can occur which results in hardware corrosion and early system and component failure. If the relative humidity is too low, computer equipment becomes susceptible to electrostatic discharge (ESD) which can cause damage to sensitive components. When monitoring the relative humidity in the data center, we recommend early warning alerts at 40% and 60% relative humidity, with critical alerts at 30% and 70% relative humidity. It is important to remember that the relative humidity is directly related to the current temperature, so monitoring temperature and humidity together is critical. As the value of IT equipment increases, the risk and associated costs can increase exponentially.

Effect of humidity on electronic devices

Problem of mould caused due to surrounding humidity
Humidity is one of the factors with heat that causes trouble in the controlling machine. How does humidity affect the controlling machine is considered below.
There are plurality of joint parts in controlling machine. Humidity is the great enemy of joint parts. Graph shows “relationship between corrosion and humidity”. It is understood that corrosion progresses rapidly when humidity exceeds 60%. Humidity of about 70% is the common level in Japan and therefore, countermeasures for humidity are extremely important in controlling machine. Moreover, corrosion progresses as temperature increases and countermeasures for heat must also be simultaneously considered along with countermeasures for humidity.
Problem of mould caused due to surrounding humidity

Ion migration
Ion migration is the phenomenon wherein metal ions are eluted from its surface when voltage is applied to metal when water molecules contained in air adhere to metal surface.
When ion migration progresses, there is danger of short circuit due to adjacent conductor(metal). Moreover, in most of the cases, circuit gets burnt by large current that flows at the instant when it makes contact with the conductor flowing, causing trouble of non-regeneration.

Water molecules contained in air adhere to the solid surface and form a thin film of water on the surface.
Ion migration

Solid (metal) surface to which voltage is applied, starts eluting as metal ions in this (abovementioned) state.

Metal eluted as ions are pulled by neighbouring conductor.

Metal film acts as a bridge between the conductors, causing short circuit thereby becoming a cause for failure.
*In most cases, the metal film is formed in dendrite shape and evaporates and disappears at the time of short circuit as it is very brittle. Therefore, failure by ion migration is a cumbersome condition which is not reproduced after occurrence.

Humidity and Computers

Environmental conditions – especially humidity – can directly affect the functioning and performance of computers…

A high level of humidity can cause internal components of PCs to rust and degrade some of their essential properties, such as electrical resistance or thermal conductivity. Under extreme conditions, humidity can cause computers to short-circuit, resulting in effects ranging from loss of data to physical damage of some system components. This situation can be aggravated further when computers are in environments that are not climate controlled such as warehouses or areas on industrial floors where other chemical vapours may be mixing with the humidity and becoming corrosive.
Computers are usually used in environments with an acceptable level of relative humidity, such as offices where conditions are controlled through air-conditioning systems. However, the same cannot be said for mobile devices or laptop computers, which can sometimes be exposed to extreme conditions. One of the most common problems is liquid getting into computers from rain, water splashed on a laptop when using it at the beach or near a swimming pool, or drinks that are accidentally spilled on them.
However, humidity can also condense inside the computer without the user realizing. This often happens when the computer is exposed to brusque changes in temperature. A typical example is when a computer is used in an air-conditioned office immediately after being transported in a vehicle exposed to direct sunlight. The same effect happens when walking for a distance outside during the winter, and then bringing the computer into a warm office – A thin film of condensation could be covering the entire interior of the laptop.
The basic measures to take in order to prevent excess humidity that can damage PCs include not using computers near liquids or where liquid can be splashed on them and not exposing them to extreme humidity. Similarly, it is also advisable to avoid brusque changes in temperature and wait for your equipment to adapt to their new conditions before switching them on. Relative humidity levels between 45% and 60% are best for computing environments. Laptops may be able to go to a more extreme 30%-80%, but never use a computer beside or near an actual humidifier .

What is a Humidity / Dew Sensor?

A humidity sensor (or hygrometer) senses, measures and reports the relative humidity in the air. It therefore measures both moisture and air temperature. Relative humidity is the ratio of actual moisture in the air to the highest amount of moisture that can be held at that air temperature. The warmer the air temperature is, the more moisture it can hold. Humidity / dew sensors use capacitive measurement, which relies on electrical capacitance. Electrical capacity is the ability of two nearby electrical conductors to create an electrical field between them. The sensor is composed of two metal plates and contains a non-conductive polymer film between them. This film collects moisture from the air, which causes the voltage between the two plates to change. These voltage changes are converted into digital readings showing the level of moisture in the air.

Adafruit Si7021 Temperature & Humidity Sensor Breakout Board

Adafruit Si7021 Temperature & Humidity Sensor Breakout Board

This lovely sensor for Silicon labs has ± 3% relative humidity measurements with a range of 0–80% RH, and ±0.4 °C temperature accuracy at a range of -10 to +85 °C. Great for all of your environmental sensing projects. It uses I2C for data transfer so it works with a wide range of microcontrollers.
We put this nice sensor on a breakout board with a 3.3V regulator and level shifting so you can use it safely with 3.3V or 5V power & logic. There's a PTFE filter to keep the sensor clean, that's the white flat thing on top. Also comes with some pin header. Some light soldering is required to attach the header but it's easy to do.

Hasil gambar untuk temperature and humidity electronic

Temperature and humidity design criteria

Use these temperature and humidity design criteria to ensure that your data center environment provides optimal conditions for your server operation.

The information technology equipment can tolerate a considerable range of temperature and humidity, as described in the server specifications for each server. Generally, the air conditioning system should be designed for 22 degrees C (71.6 degrees F) and 45 percent relative humidity at altitudes up to 2150 m (7000 ft.). This design point provides for the largest buffer in terms of available system time. If the air conditioning system fails or malfunctions, the computer will be able to operate until it reaches its specified limits. This buffer provides additional time for air conditioning repairs before the computer must be shut down. The design point has also been proven to be a generally acceptable personal comfort level.

The design points for temperature and relative humidity might differ in certain geographical areas.

Air conditioning control instruments that respond to + or - 1 degree C ( + or - 2 degrees F) temperature and + or - 5 percent relative humidity should be installed.

Computer room cooling is basically a sensible (as opposed to a latent) cooling operation. (Sensible heat is defined as the transfer of thermal energy to or from a substance resulting in a change in temperature: Latent heat is the thermal energy absorbed or evolved in a process other than change of temperature.)

Substantial deviations from the recommended design point in either direction, if maintained for long periods (that is, for hours), will expose the system to malfunction from external conditions. For example, high relative humidity levels might cause improper feeding of paper, operator discomfort, and condensation on windows and walls when outside temperatures fall below room dew point.

Low relative humidity levels alone will not cause static discharge. However, in combination with many types of floor construction, floor coverings, and furniture, static charges that are generated by movement of people, carts, furniture, and paper will be more readily stored on one or more of the objects. These charges might be high enough to be objectionable to operating personnel, if discharged by contact with another person or object. If discharged to or near information technology equipment or other electronic equipment, these charges can cause intermittent interference. In most areas, it will be necessary to add moisture to the room air to meet the design criteria.

Because temperature or relative humidity deviations for only a few hours will cause the floors, desks, furniture, cards, tapes, and paper to reach a condition that will readily permit the retention of a charge, it is recommended that the air conditioning system be automatically controlled and provided with a high or low alarm or a continuous recording device with the appropriate limits marked.

Server operating limits

Some individual servers might require special consideration and have more or less restrictive requirements. See your server specifications for specific environmental limits.

The typical server operating environment is shown in the following table. The server nonoperating limits are shown in the following Nonoperating Server Limits table.

Table 1. Typical server operating environment
Environmental criteria	Computer room limits	Office space air conditioned	Office space not air conditioned
Temperature	16 to 32 degrees C (60.8 to 89.6 degrees F)	16 to 32 degrees C (60.8 to 89.6degrees F)	10.0 to 40.6 degrees C (50 to 105.08 degrees F)
Relative humidity	20 to 80 percent	8 to 80 percent	8 to 80 percent
Maximum wet bulb	23 degrees C (73.4 degrees F)	23 degrees C (73.4 degrees F)	27.0 degrees C (80.6 degrees F)

The design criteria is shown is the following table.

Table 2. Design criteria
Environmental criteria	Design criteria
Temperature	22 degrees C (71.6 degrees F)
Relative humidity	45 percent
Maximum wet bulb	23 degrees C (73.4 degrees F)

The recommended design is shown in the following figure.

Figure 1. Recommended design

Note

The air entering the server must be at the conditions for operation before power is turned on. Under no circumstances may the server's input air, room air, or humidity exceed the upper limit of the operating conditions. This is the maximum operating temperature limit and should not be considered a design condition. Also, the relative humidity of the air entering the server should not be greater than 80 percent. This specification is an absolute maximum. The optimum condition is where the room is at the design criteria of 22 degrees C (71.6 degrees F) and 45 percent humidity.

Air temperature in a duct or an underflow air supply should be kept above the room dew point temperature to prevent condensation within or on the servers. When it is necessary to add moisture to the system for control of low relative humidity, one of the following methods should be used:

Steam grid or jets
Evaporation pan or pane
Steam cup
Water atomizers

Water treatment might be necessary in areas with high mineral content to avoid contamination of the air.

Note

In localities where the outside temperature drops below freezing, condensation will form on single, glazed window panes. Also, if outside temperatures are considerably below freezing, the outside walls of the building should be waterproofed or vapor sealed on the inside or, in time, structural damage will occur in the outside walls.

Server nonoperating limits

When the facilities are shut down, the nonoperating environmental specifications must be followed to prevent damage to the server and to ensure reliable operation when power is restored.

Table 3. Nonoperating server limits
	Server nonoperating limits
Temperature	10 to 43 degrees C (50 to 109.4 degrees F)
Relative humidity	8 to 80 percent
Maximum wet bulb	27 degrees C (80.6 degrees F)

Humidity and ESD Control

INTRODUCTION
The control of electrostatic discharge can easily be implemented by employing basic control practices and principles in conjunction with the proper control products. Establishing an ESD Control program is dependent on the components that need protecting, the specifications of the internal quality control program and both the manufacturer and customer's requirements. What is often overlooked are the inherent environmental conditions and their control, i.e., humidity, temperature, pressure, number of air borne particles and air recirculation. The most significant environmental factor in ESD Control is the relative humidity (RH).
EFFECTS OF HUMIDITYIn very dry areas, humidification is desirable because it makes antistatic materials with "sweat layers" function better as well as an overall reduction (not elimination) in triboelectric charging for all materials. Do not let high humidity levels build a false confidence, and beware of corrosion problems with interconnects and other electrical interfaces.
A high relative humidity, over 30% RH, reduces the resistance of most dielectrics resulting in an increase in return current, which is the current that opposes a charge buildup. When an object is undergoing tribocharging in a high humidity environment, the object will reach an equilibrium point where the tribocharging current equals the return current. For objects that undergo charging to a high potential, the primary impact of humidity is to encourage or discourage corona, and effect the rise time of the discharge current.
Normally, the moisture content in the air tends to lower the surface resistance of floors, carpets, table mats, etc., by letting wet particles create a vaguely conductive (or less than 10^-9 Ohms/square) film over an otherwise insulating surface. If the relative humidity decreases, this favorable phenomenon disappears.
The air itself, being dry, becomes a part of the electrostatic build-up mechanism every time there is an air flow (wind, air conditioning, blower) passing over an insulated surface.

Table I

Tribocharging and Relative Humidity (RH)

(Reference 4)

ACTIVITY (@ 70° F)	STATIC VOLTAGES
ACTIVITY (@ 70° F)	20 % RH	80% RH
Walking across vinyl floor	12 kV	250 V
Walking across synthetic carpet	35 kV	1.5 kV
Arising from foam cushion	18 kV	1.5 kV
Picking up polyethylene bag	20 kV	600 V
sliding styrene box on carpet	18 kV	1.5 kV
Removing Mylar tape from PC board	12 kV	1.5 kV
Shrinkable film on PC board	16 kV	3 kV
Triggering vacuum solder remover	8 kV	1 kV
Aerosol circuit freeze spray	15 kV	5 kV

As Table 1 above shows, triboelectric charging persists even at high relative humidity. The fact remains that triboelectric charging becomes troublesome below 20 to 30% relative humidity, as shown by the high voltages attained at 20% RH in the Table 1. According to Koyler ET. Al. [1], Relative humidity values should include an associated temperature because a temperature factor is involved in surface resistivity. MIL-HDBK-263 Standard Humid air helps to dissipate electrostatic charges by keeping surfaces moist, therefore increasing surface conductivity. Substantial electrostatic voltage levels can accumulate with a decrease in relative humidity, see Table 1 above. However, it is also evident from Table 1 that significant electrostatic voltages can still be generated with relative humidity as high as 90 percent. Relative humidity between 40 percent and 60 percent in ESD protective areas is desirable as long as it does not result in corrosion or in other detrimental effects such as PWB delamination during soldering. Where high relative humidity levels cannot be maintained, ionized air can be used to dissipate electrostatic charges.
MIL-STD-1695 specifically addresses relative humidity levels in the range of 30 - 70 percent in areas where electronic parts and hybrid microcircuits (MIL-STD-1695, bwork areas 5 and 6) are handled or processed. MIL-STD-1695 requires the same level of relative humidity controls for handling and storage areas (MIL-STD-1695, work area 13), except when items are covered or protected. CONCLUSION Humidity control does limit the triboelectric charging process, but does not eliminate any of the conventional safeguards; it is strictly a backup or "safety net" measure. Also, humidity control may give personnel a false sense of security and cause a relaxation of operator disciplines, thus lowering overall ESD safety. Humidity control is also expensive and can cause corrosion or other adverse side effects. Humidity control is a backup that should be implemented only after careful consideration of benefits vs. cost and hazards. Humidification to 30 or 40% relative humidity, minimum, at 70° F, is surely desirable, but drawbacks include (1) expense of facilities for adding water to the air, (2) possible adverse effects such as delamination of polyamide circuit-board laminates or corrosion of metals if the humidity becomes too high, (3) the psychological factor of false confidence inspired in operators and even engineers, and (4) personnel discomfort. An ESD control program should still be employed using conventional grounding, shielding, ionization, and training products and techniques.

Best humidity level for electronic shops?

What is the best humidity level for an electronic shop? On one end of the scale, you will have problems from corrosion due to high humidity and condensation, but at the other end there will be serious problems from ESD.

I've worked in shops at either extreme end of the scale, and would imagine the ideal level being around 50% relative humidity. Thoughts?

Just working with grounded wrist-straps, and keeping major ESD generating clutter to a minimum, you shouldn't have much problem down to about 40% relative humidity. However, below 35% or 40%, you should start being extra vigilant.

For example, it's always a good idea to keep styro foam packing material, wool sweaters, polyester fleeces, and rolls of packing tape away from your ESD-safe work area, but when the humidity is very low, even ordinary paper can start to be a problem. An ordinary laminated surface that might be passable at high humidity can start to cause problems when the air gets very dry. The professionals use grounded mats on the workbench surface all the time. When the air is very dry, ionizing fans become necessary.

So, you can work with almost any R.H., depending on the level of protection measures you have in place.

Humidity

Humidity is the amount of water vapor present in the air. Water vapor is the gaseous state of water and is invisible to the human eye.^[1] Humidity indicates the likelihood of precipitation, dew, or fog. Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. This effect is calculated in a heat index table or humidex. The amount of water vapor that is needed to achieve saturation increases as the temperature increases. As the temperature of a parcel of water becomes lower it will eventually reach the point of saturation without adding or losing water mass. The differences in the amount of water vapor in a parcel of air can be quite large. For example, a parcel of air that is near saturation may contain 28 grams of water per cubic meter of air at 30 °C, but only 8 grams of water per cubic meter of air at 8 °C.
There are three main measurements of humidity: absolute, relative and specific. Absolute humidity is the water content of air expressed in gram per cubic meter.^[2] Relative humidity, expressed as a percent, measures the current absolute humidity relative to the maximum (highest point) for that temperature. Specific humidity is the ratio of the mass of water vapor to the total mass of the moist air parcel.

Humidity and hygrometry
Types Paranal Observatory on Cerro Paranal in the Atacama Desert is one of the driest places on earth. Absolute humidity Absolute humidity is the total mass of water vapor present in a given volume of air. It does not take temperature into consideration. Absolute humidity in the atmosphere ranges from near zero to roughly 30 grams per cubic meter when the air is saturated at 30 °C (86 °F).^[4] Absolute humidity is the mass of the water vapor $(m_{H_{2}O})$ , divided by the volume of the air and water vapor mixture $(V_{net})$ , which can be expressed as: $AH={\frac {m_{H_{2}O}}{V_{net}}}.$ The absolute humidity changes as air temperature or pressure changes. This makes it unsuitable for chemical engineering calculations, e.g. for clothes dryers, where temperature can vary considerably. As a result, absolute humidity in chemical engineering may refer to mass of water vapor per unit mass of dry air, also known as the mass mixing ratio (see "specific humidity" below), which is better suited for heat and mass balance calculations. Mass of water per unit volume as in the equation above is also defined as volumetric humidity. Because of the potential confusion, British Standard BS 1339 (revised 2002) suggests avoiding the term "absolute humidity". Units should always be carefully checked. Many humidity charts are given in g/kg or kg/kg, but any mass units may be used. The field concerned with the study of physical and thermodynamic properties of gas–vapor mixtures is named psychrometrics. Relative humidity The relative humidity $(RH$ or $\phi )$ of an air-water mixture is defined as the ratio of the partial pressure of water vapor $(p_{H_{2}O})$ in the mixture to the equilibrium vapor pressure of water $(p_{H_{2}O}^{})$ over a flat surface of pure water^[5] at a given temperature: $\phi ={p_{H_{2}O} \over p_{H_{2}O}^{}}$ Relative humidity is normally expressed as a percentage; a higher percentage means that the air-water mixture is more humid. Relative humidity is an important metric used in weather forecasts and reports, as it is an indicator of the likelihood of precipitation, dew, or fog. In hot summer weather, a rise in relative humidity increases the apparent temperature to humans (and other animals) by hindering the evaporation of perspiration from the skin. For example, according to the Heat Index, a relative humidity of 75% at air temperature of 80.0 °F (26.7 °C) would feel like 83.6 °F ±1.3 °F (28.7 °C ±0.7 °C).^[8]^[9] Specific humidity Specific humidity (or moisture content) is the ratio of the mass of water vapor to the total mass of the moist air parcel.^[10] Specific humidity is approximately equal to the "mixing ratio", which is defined as the ratio of the mass of water vapor in an air parcel to the mass of dry air for the same parcel. As temperature decreases, the amount of water vapor needed to reach saturation also decreases. As the temperature of a parcel of air becomes lower it will eventually reach the point of saturation without adding or losing water mass. The differences in the amount of water vapor in a parcel of air can be quite large, for example; A parcel of air that is near saturation may contain 28 grams of water per cubic meter of air at 30 °C, but only 8 grams of water per cubic meter of air at 8 °C. Measurement A hygrometer A device used to measure humidity is called a psychrometer or hygrometer. A humidistat is a humidity-triggered switch, often used to control a dehumidifier. There are various devices used to measure and regulate humidity. Calibration standards for the most accurate measurement include the gravimetric hygrometer, chilled mirror hygrometer, and electrolytic hygrometer. The gravimetric method, while the most accurate, is very cumbersome. For fast and very accurate measurement the chilled mirror method is effective.^[11] Humidity is also measured on a global scale using remotely placed satellites. These satellites are able to detect the concentration of water in the troposphere at altitudes between 4 and 12 kilometers. Satellites that can measure water vapor have sensors that are sensitive to infrared radiation. Water vapor specifically absorbs and re-radiates radiation in this spectral band. Satellite water vapor imagery plays an important role in monitoring climate conditions (like the formation of thunderstorms) and in the development of weather forecasts. Climate While humidity itself is a climate variable, it also interacts strongly with other climate variables. The humidity is affected by winds and by rainfall. The most humid cities on earth are generally located closer to the equator, near coastal regions. Cities in South and Southeast Asia are among the most humid. Kuala Lumpur, Jakarta, and Singapore have very high humidity all year round because of their proximity to water bodies and the equator and often overcast weather. Some places experience extreme humidity during their rainy seasons combined with warmth giving the feel of a lukewarm sauna, such as Kolkata, Chennai and Cochin in India, and Lahore in Pakistan. Sukkur city located on the Indus River in Pakistan has some of the highest and most uncomfortable dew point in the country frequently exceeding 30 °C (86 °F) in the Monsoon season.^[12] High temperatures couple up with bizarre dew point to create heat index in excess of 65 °C (149 °F). Darwin, Australia experiences an extremely humid wet season from December to April. Shanghai and Hong Kong in China also have an extreme humid period in their summer months. During the South-west and North-east Monsoon seasons (respectively, late May to September and November to March), expect heavy rains and a relatively high humidity post-rainfall. Outside the monsoon seasons, humidity is high (in comparison to countries North of the Equator), but completely sunny days abound. In cooler places such as Northern Tasmania, Australia, high humidity is experienced all year due to the ocean between mainland Australia and Tasmania. In the summer the hot dry air is absorbed by this ocean and the temperature rarely climbs above 35 °C (95 °F). United States In the United States the most humid cities, strictly in terms of relative humidity, are Forks and Olympia, Washington.^[13] This fact may come as a surprise to many, as the climate in this region rarely exhibits the discomfort usually associated with high humidity. This is because high dew points play a more significant role than relative humidity in discomfort, and so the air in these western cities usually does not feel "humid" as a result. In general, dew points are much lower in the Western U.S. than those in the Eastern U.S. The highest dew points in the US are found in coastal Florida and Texas. When comparing Key West and Houston, two of the most humid cities from those states, coastal Florida seems to have the higher dew points on average. However, Houston lacks the coastal breeze present in Key West, and, as a much larger city, it suffers from the urban heat island effect.^[14] A dew point of 88 °F (31 °C) was recorded in Moorhead Minnesota on July 19, 2011, with a heat index of 133.5, although dew points over 80 °F (27 °C) are rare there.^[15] The US city with the lowest annual humidity is Las Vegas, Nevada, averaging 39% for a high and 21% as a low.^[16] Appleton, Wisconsin registered a dew point of 90 degrees F on 13 July 1995 with an air temperature of 104 degrees resulting in a heat index of 149 degrees; this record has apparently held and in fact the highest dew point measured in the country bounced amongst or was tied by locations in Wisconsin, Minnesota, and Iowa during the preceding 70 years or more with locations in northern Illinois also coming close. Dew points of 95 degrees are found on the Red Sea coast of Saudi Arabia at certain times. Global climate Humidity affects the energy budget and thereby influences temperatures in two major ways. First, water vapor in the atmosphere contains "latent" energy. During transpiration or evaporation, this latent heat is removed from surface liquid, cooling the earth's surface. This is the biggest non-radiative cooling effect at the surface. It compensates for roughly 70% of the average net radiative warming at the surface. Second, water vapor is the most abundant of all greenhouse gases. Water vapor, like a green lens that allows green light to pass through it but absorbs red light, is a "selective absorber". Along with other greenhouse gases, water vapor is transparent to most solar energy, as you can literally see. But it absorbs the infrared energy emitted (radiated) upward by the earth's surface, which is the reason that humid areas experience very little nocturnal cooling but dry desert regions cool considerably at night. This selective absorption causes the greenhouse effect. It raises the surface temperature substantially above its theoretical radiative equilibrium temperature with the sun, and water vapor is the cause of more of this warming than any other greenhouse gas. Unlike most other greenhouse gases, however, water is not merely below its boiling point in all regions of the Earth, but below its freezing point at many altitudes. As a condensible greenhouse gas, it precipitates, with a much lower scale height and shorter atmospheric lifetime- weeks instead of decades. Without other greenhouse gases, Earth's blackbody temperature, below the freezing point of water, would cause water vapor to be removed from the atmosphere. Water vapor is thus a "slave" to the non-condensible greenhouse gases. Air density and volume Humidity depends on water vaporization and condensation, which, in turn, mainly depends on temperature. Therefore, when applying more pressure to a gas saturated with water, all components will initially decrease in volume approximately according to the ideal gas law. However, some of the water will condense until returning to almost the same humidity as before, giving the resulting total volume deviating from what the ideal gas law predicted. Conversely, decreasing temperature would also make some water condense, again making the final volume deviate from predicted by the ideal gas law. Therefore, gas volume may alternatively be expressed as the dry volume, excluding the humidity content. This fraction more accurately follows the ideal gas law. On the contrary the saturated volume is the volume a gas mixture would have if humidity was added to it until saturation (or 100% relative humidity). Humid air is less dense than dry air because a molecule of water (M ≈ 18 u) is less massive than either a molecule of nitrogen (M ≈ 28) or a molecule of oxygen (M ≈ 32). About 78% of the molecules in dry air are nitrogen (N₂). Another 21% of the molecules in dry air are oxygen (O₂). The final 1% of dry air is a mixture of other gases. For any gas, at a given temperature and pressure, the number of molecules present in a particular volume is constant – see ideal gas law. So when water molecules (vapor) are introduced into that volume of dry air, the number of air molecules in the volume must decrease by the same number, if the temperature and pressure remain constant. (The addition of water molecules, or any other molecules, to a gas, without removal of an equal number of other molecules, will necessarily require a change in temperature, pressure, or total volume; that is, a change in at least one of these three parameters. If temperature and pressure remain constant, the volume increases, and the dry air molecules that were displaced will initially move out into the additional volume, after which the mixture will eventually become uniform through diffusion.) Hence the mass per unit volume of the gas—its density—decreases. Isaac Newton discovered this phenomenon and wrote about it in his book Opticks. Effects Animals and plant Humidity is one of the fundamental abiotic factors that defines any habitat, and is a determinant of which animals and plants can thrive in a given environment.^[24] The human body dissipates heat through perspiration and its evaporation. Heat convection, to the surrounding air, and thermal radiation are the primary modes of heat transport from the body. Under conditions of high humidity, the rate of evaporation of sweat from the skin decreases. Also, if the atmosphere is as warm as or warmer than the skin during times of high humidity, blood brought to the body surface cannot dissipate heat by conduction to the air, and a condition called hyperthermia results. With so much blood going to the external surface of the body, less goes to the active muscles, the brain, and other internal organs. Physical strength declines, and fatigue occurs sooner than it would otherwise. Alertness and mental capacity also may be affected, resulting in heat stroke or hyperthermia. Human comfort Humans are sensitive to humid air because the human body uses evaporative cooling as the primary mechanism to regulate temperature. Under humid conditions, the rate at which perspiration evaporates on the skin is lower than it would be under arid conditions. Because humans perceive the rate of heat transfer from the body rather than temperature itself, we feel warmer when the relative humidity is high than when it is low. Some people experience difficulty breathing in humid environments. Some cases may possibly be related to respiratory conditions such as asthma, while others may be the product of anxiety. Sufferers will often hyperventilate in response, causing sensations of numbness, faintness, and loss of concentration, among others.^[25] Air conditioning reduces discomfort in the summer not only by reducing temperature, but also by reducing humidity. In winter, heating cold outdoor air can decrease relative humidity levels indoor to below 30%,^[26] leading to discomfort such as dry skin, cracked lips and excessive thirst. Electronics Many electronic devices have humidity specifications, for example, 5% to 45%. At the top end of the range, moisture may increase the conductivity of permeable insulators leading to malfunction. Too low humidity may make materials brittle. A particular danger to electronic items, regardless of the stated operating humidity range, is condensation. When an electronic item is moved from a cold place (e.g. garage, car, shed, an air conditioned space in the tropics) to a warm humid place (house, outside tropics), condensation may coat circuit boards and other insulators, leading to short circuit inside the equipment. Such short circuits may cause substantial permanent damage if the equipment is powered on before the condensation has evaporated. A similar condensation effect can often be observed when a person wearing glasses comes in from the cold (i.e. the glasses become foggy).^[27] It is advisable to allow electronic equipment to acclimatise for several hours, after being brought in from the cold, before powering on. Some electronic devices can detect such a change and indicate, when plugged in and usually with a small droplet symbol, that they cannot be used until the risk from condensation has passed. In situations where time is critical, increasing air flow through the device's internals, such as removing the side panel from a PC case and directing a fan to blow into the case, will reduce significantly the time needed to acclimatise to the new environment. In contrast, a very low humidity level favors the build-up of static electricity, which may result in spontaneous shutdown of computers when discharges occur. Apart from spurious erratic function, electrostatic discharges can cause dielectric breakdown in solid state devices, resulting in irreversible damage. Data centers often monitor relative humidity levels for these reasons. Building construction Common construction methods often produce building enclosures with a poor thermal boundary, requiring an insulation and air barrier system designed to retain indoor environmental conditions while resisting external environmental conditions.^[28] The energy-efficient, heavily sealed architecture introduced in the 20th century also sealed off the movement of moisture, and this has resulted in a secondary problem of condensation forming in and around walls, which encourages the development of mold and mildew. Additionally, buildings with foundations not properly sealed will allow water to flow through the walls due to capillary action of pores found in masonry products. Solutions for energy-efficient buildings that avoid condensation are a current topic of architecture. Industry High humidity can often have a negative effect on the capacity of chemical plants and refineries that use furnaces as part of the process (e.g. steam reforming, wet sulfuric acid process). The humidity will reduce the oxygen concentration, and the flue gas fans have to pull more air through the system to get the same firing rate (dry air is 20.9% oxygen, at 100% relative humidity the air is 20.4% oxygen). Is Humid Weather Bad for a Computer? Yes, Humid Weather is bad for your Computer, with many houses here on the Gold Coast along the Coast and along man made canals this allows the issue to reach further inland. Tips for Avoiding Moisture & Corrosion. It is true that salt air will corrode hardware and electronics especially near the ocean/coast. Whether you prefer a laptop or a desktop your PC/Mac is affected by its environment. While overly dry conditions can cause static electricity in your computer’s components, excessively humid conditions can cause faster corrosion and internal damage. If your environment is especially humid you should take precautions to protect your computer from damage due to moisture. Take note of the general level of humidity and follow these simple steps to stop damage. Install a dehumidifier in your home or office. Dehumidifiers remove moisture in the air so it’s safer to use your desktop, laptop or tablet PC. When using a dehumidifier remember to empty out the reservoir regularly to ensure that the machine works efficiently. In our Office we use Hippos which may work for some, others may need to invest in domestic or commercial stand-alone models. Situate your computer in an area of the home or office with a controlled temperature. Avoid using your computer in humid areas such as in the Bathroom, Laundry or Outside by the Ocean. Condensation from the humidity can affect the internal components of your computer causing corrosion or sudden malfunction. Keep your computer stationary whenever possible. One way humidity builds up in your computer is when you experience sudden temperature changes. For instance, going from the cold winter air to a warm office could cause condensation. Transport your computer as little as possible and always use an insulated case to protect it from extreme temperatures if you must travel with it. Wipe your computer down quickly if you notice moisture on the outside of the case. Use a clean towel to remove outer moisture before it has time to seep into the computer through the keyboard or vents. For this very reason, avoid positioning your computer near windows or external doors. Iron rust is red/brown, aluminium rust is white, copper corrosion is blue/green. We recommend for clients living along the Gold Coast that they get regular checkups, this ensures your PC is kept dust free and helps to prevent corrosion and overheating. We can perform the clean onsite or in our workshop, we will also inspect your components for surface corrosion or salt buildup which is a big killer of video cards. Data logger A data logger (also datalogger or data recorder) is an electronic device that records data over time or in relation to location either with a built in instrument or sensor or via external instruments and sensors. Increasingly, but not entirely, they are based on a digital processor (or computer). They generally are small, battery powered, portable, and equipped with a microprocessor, internal memory for data storage, and sensors. Some data loggers interface with a personal computer, and use software to activate the data logger and view and analyze the collected data, while others have a local interface device (keypad, LCD) and can be used as a stand-alone device. Data loggers vary between general purpose types for a range of measurement applications to very specific devices for measuring in one environment or application type only. It is common for general purpose types to be programmable; however, many remain as static machines with only a limited number or no changeable parameters. Electronic data loggers have replaced chart recorders in many applications. One of the primary benefits of using data loggers is the ability to automatically collect data on a 24-hour basis. Upon activation, data loggers are typically deployed and left unattended to measure and record information for the duration of the monitoring period. This allows for a comprehensive, accurate picture of the environmental conditions being monitored, such as air temperature and relative humidity. The cost of data loggers has been declining over the years as technology improves and costs are reduced. Simple single channel data loggers cost as little as $25. More complicated loggers may costs hundreds or thousands of dollars. Data logger Cube storing Small data logger with integrated sensors measuring temperature, pressure, humidity, light and 3-axis acceleration technical and sensor data Data formats Standardisation of protocols and data formats has been a problem but is now growing in the industry and XML, JSON, and YAML are increasingly being adopted for data exchange. The development of the Semantic Web and the Internet of Things is likely to accelerate this present trend. Instrumentation protocols Several protocols have been standardised including a smart protocol, SDI-12, that allows some instrumentation to be connected to a variety of data loggers. The use of this standard has not gained much acceptance outside the environmental industry. SDI-12 also supports multi drop instruments. Some datalogging companies are also now supporting the MODBUS standard. This has been used traditionally in the industrial control area, and there are many industrial instruments which support this communication standard. Another multi drop protocol which is now starting to become more widely used is based upon CAN Bus (ISO 11898). Some data loggers use a flexible scripting environment to adapt themselves to various non-standard protocols. Data logging versus data acquisition The terms data logging and data acquisition are often used interchangeably. However, in a historical context they are quite different. A data logger is a data acquisition system, but a data acquisition system is not necessarily a data logger. Data loggers typically have slower sample rates. A maximum sample rate of 1 Hz may be considered to be very fast for a data logger, yet very slow for a typical data acquisition system. Data loggers are implicitly stand-alone devices, while typical data acquisition system must remain tethered to a computer to acquire data. This stand-alone aspect of data loggers implies on-board memory that is used to store acquired data. Sometimes this memory is very large to accommodate many days, or even months, of unattended recording. This memory may be battery-backed static random access memory, flash memory or EEPROM. Earlier data loggers used magnetic tape, punched paper tape, or directly viewable records such as "strip chart recorders". Given the extended recording times of data loggers, they typically feature a mechanism to record the date and time in a timestamp to ensure that each recorded data value is associated with a date and time of acquisition in order to produce a sequence of events. As such, data loggers typically employ built-in real-time clocks whose published drift can be an important consideration when choosing between data loggers. Data loggers range from simple single-channel input to complex multi-channel instruments. Typically, the simpler the device the less programming flexibility. Some more sophisticated instruments allow for cross-channel computations and alarms based on predetermined conditions. The newest of data loggers can serve web pages, allowing numerous people to monitor a system remotely. The unattended and remote nature of many data logger applications implies the need in some applications to operate from a DC power source, such as a battery. Solar power may be used to supplement these power sources. These constraints have generally led to ensure that the devices they market are extremely power efficient relative to computers. In many cases they are required to operate in harsh environmental conditions where computers will not function reliably. Portable Dataloggers may reach up to 20 channels with maximum 10ms (100Hz) sampling rate. This unattended nature also dictates that data loggers must be extremely reliable. Since they may operate for long periods nonstop with little or no human supervision, and may be installed in harsh or remote locations, it is imperative that so long as they have power, they will not fail to log data for any reason. Manufacturers go to great length to ensure that the devices can be depended on in these applications. As such dataloggers are almost completely immune to the problems that might affect a general-purpose computer in the same application, such as program crashes and the instability of some operating systems. Applications Data logger application for weather station at P2I LIPI Applications of data logging include: Unattended weather station recording (such as wind speed / direction, temperature, relative humidity, solar radiation). Unattended hydrographic recording (such as water level, water depth, water flow, water pH, water conductivity). Unattended soil moisture level recording. Unattended gas pressure recording. Offshore buoys for recording a variety of environmental conditions. Road traffic counting. Measure temperatures (humidity, etc.) of perishables during shipments: Cold chain.^[1] Measure variations in light intensity. Process monitoring for maintenance and troubleshooting applications. Process monitoring to verify warranty conditions Wildlife research with pop-up archival tags Measure vibration and handling shock (drop height) environment of distribution packaging.^[2] Tank level monitoring. Deformation monitoring of any object with geodetic or geotechnical sensors controlled by an automatic deformation monitoring system. Environmental monitoring. Vehicle Testing (including crash testing) Motor Racing Monitoring of relay status in railway signalling. For science education enabling 'measurement', 'scientific investigation' and an appreciation of 'change' Record trend data at regular intervals in veterinary vital signs monitoring. Load profile recording for energy consumption management. Temperature, humidity and power use for heating and air conditioning efficiency studies. Water level monitoring for groundwater studies. Digital electronic bus sniffer for debug and validation Examples Black-box (stimulus/response) loggers: A flight data recorder (FDR), a piece of recording equipment used to collect specific aircraft performance data. The term may also be used, albeit less accurately, to describe the cockpit voice recorder (CVR), another type of data recording device found on board aircraft. An event data recorder (EDR), a device installed by the manufacturer in some automobiles which collects and stores various data during the time-frame immediately before and after a crash. A voyage data recorder (VDR), a data recording system designed to collect data from various sensors on board a ship. A train event recorder, a device that records data about the operation of train controls and performance in response to those controls and other train control systems. In automobiles, all diagnostic trouble codes (DTCs) are logged in engine control units (ECUs) so that at the time of service of a vehicle, a service engineer will read all the DTCs using Tech-2 or similar tools connected to the on-board diagnostics port, and will come to know problems occurred in the vehicle. Sometimes a small OBD data logger is plugged into the same port to continuously record vehicle data. In embedded system and digital electronics design, specialized high-speed digital data logger help overcome the limitations of more traditional instruments such as the oscilloscope and the logic analyzer. The main advantage of a data logger is its ability to record very long traces, which proves very useful when trying to correct functional bugs that happen once in while. In the racing industry, Data Loggers are used to record data such as braking points, lap/sector timing, and track maps, as well as any on-board vehicle sensors. Health data loggers: The growing, preparation, storage and transportation of food. Data logger is generally used for data storage and these are small in size. A Holter monitor is a portable device for continuously monitoring various electrical activity of the cardiovascular system for at least 24 hours. Electronic health record loggers. Other general data acquisition loggers: An (scientific) experimental testing data acquisition tool. Ultra Wideband Data Recorder, high-speed data recording up to 2 GigaSamples per second. An open source data logger based on the Raspberry Pi computer Future directions Data Loggers are changing more rapidly now than ever before. The original model of a stand-alone data logger is changing to one of a device that collects data but also has access to wireless communications for alarming of events, automatic reporting of data and remote control. Data loggers are beginning to serve web pages for current readings, e-mail their alarms and FTP their daily results into databases or direct to the users. Very recently, there is a trend to move away from proprietary products with commercial software to open source software and hardware devices. The Raspberry Pi single-board computer is among others a popular platform hosting real-time Linux or preemptive-kernel Linux operating systems with many digital interfaces like I2C, SPI or UART enabling the direct interconnection of a digital sensor and a computer, and unlimited number of configurations to show measurements in real-time over the internet, process data, plot charts and diagrams... There are more and more community-developed (open source) projects for data acquisition / data logging A temperature data logger, also called temperature monitor, is a portable measurement instrument that is capable of autonomously recording temperature over a defined period of time. The digital data can be retrieved, viewed and evaluated after it has been recorded. A data logger is commonly used to monitor shipments in a cold chain and to gather temperature data from diverse field conditions. A variety of constructions are available. Most have an internal thermistor or thermocouple or can be connected to external sources. Sampling and measurement are periodically taken and digitally stored. Some have a built in display of data or out-of-tolerance warnings. Data retrieval can be by cable, RFID, wireless systems, etc. They generally are small, battery powered, portable, and equipped with a microprocessor, internal memory for data storage, and sensors. Some data loggers interface with personal computers or smart phones for set-up, control, and analysis. Some include other sensors such as relative humidity, wind, light, etc. Others may record input from GPS devices. Depending on the use, governing quality management systems sometimes require calibration to national standards and compliance with formal verification and validation protocols Choices of temperature data loggers can be based on many factors, such as: Cost Reusability Battery life Ease of use; set-up, readability, download data, analysis, etc. Temperature range Number of measurements stored Accuracy and precision - degree of agreement of recorded temperature with actual Resolution Response time – the time required to measure 63.2% of the total difference between its initial and final temperature when subjected to a step function change in temperature; other points such as 90% are also used.^[2] shock and vibration resistance Water resistance – humidity, condensation, etc. Size, weight, mounting Certifications, calibrations, etc. Software Data export Data integration with other systems Uses Environmental monitoring Autonomous data loggers can be taken to diverse locations that cannot easily support fixed temperature monitoring equipment.^[3] These might include: mountains, deserts, jungles, mines, ice flows, caves, etc. Portable data loggers are also used in industry and laboratory situations where stand-alone recording is desired. Monitor shipments Temperature sensitive products such as foods,^[4] pharmaceuticals,^[5] and some chemicals are often monitored during shipment and logistics operations. Exposure to temperatures outside of an acceptable range, for a critical time period, can degrade the product or shorten shelf life. Regulations and contracts make temperature monitoring mandatory for some products. Data loggers are often small enough to be placed inside an insulated shipping container or directly attached to a product inside a refrigerator truck or a refrigerated container. These monitor the temperature of the product being shipped. Some data loggers are placed on the outside of the package or in the truck or intermodal container to monitor the air temperature. Placement of data loggers and sensors is critical: Studies have shown that temperatures inside a truck or intermodal container are strongly affected by proximity to exterior walls and roof and to locations on the lading. Modern digital data loggers are very portable and record the actual times and temperatures. This information can be used to model product degradation and to pinpoint the location and cause of excessive exposure. The measured data reveals whether the goods in transit have been subjected to potentially damaging temperature extremes or an excessive Mean kinetic temperature. Based on this data, the options may be: If there have not been out of tolerance temperatures for critical times, continue to use the shipment, without special inspection If potentially damaging temperature hazards have occurred, thoroughly inspect the shipment for damage or degradation. Possibly accelerate sale and use because of reduced shelf life.^[8] The consignee may negotiate with the carrier or shipper or even choose to reject a shipment where sensors indicate severe temperature history The time of the temperature extreme, or GPS tracking, may be able to determine the location of the infraction to direct appropriate corrective action. Multiple replicate shipments of data loggers are also used to compare modes of shipment (routes, vendors) and to develop composite data to be used in package testing protocols =================THUMBLERER DEBT COSTING ===================