Dehumidification Basics 101 - Manchester Total Air

1 DehumidificationBasics101 Tech to Tech Column April 08 Make daily deposits to your box of knowledge, soon it will have manyreference cards. --Randal S. RipleySpring has finally reached New Englandand I don t knowaboutyou but this winterseemed many technical columns will focuson air conditioning start upand/or service,I thought I would go with something different know in simple terms thathumidityis water vapor in the air. We also knowthat warmair can hold more water vapor than cold air and thatrelative humidityis the ratio of water vapor inthe air to the amountof water vaporthe air can hold at a s(American Society Heating Refrigeration Air conditioning Engineers)published optimal comfort zone for relative humidity is 30-60%.

2 Dustmites that cause allergiescan be bestcontrolled below 50%.High relative humidity levels of 60% or higheron a hot daycan make a human beinguncomfortableto miserable(in my case). The reason for this is that we are human furnaces thatarealways releasing heat and never absorbing it. When it is hot and there is little temperaturedifference between your body and the ambient temperature,your body tries to release heatthrough another one of its cooling mechanisms evaporative cooling or sweating as we call evaporative coolingsystemsworks well on days with low relative humidity and inplaces like Las Vegas with its very low relative humidity.

3 You may not even realize you aresweating because the water evaporates so whenit is hot and the relative humidity is high making it sothatyour body can tevaporate this water to theair that is already saturated and can t hold much more water vapor;this moisture is not going to evaporate from your skinleaving you soaked and those hot & humid days that we humans need relief from the unbearable humidity, weuse ourair conditioning systems that coolsthe air temperature(sensible heat removal)and alsoremovessome humidity(latent heat)from the air as a function of its levels of humidity can cause mold, mildew and bacteriaand mold growth is agrowing problem in today stighter homes and can be quitea tenaciousfoe to defeat once it addition to this,it has a detrimentaleffect on our belongings, especially those instorage facilities or the basement.

4 Books, clothing,and otherbelongings can turn yellow, smellbadly and develop mold growth on them. The Dehumidification Handbook Second Edition, published by Muntersof Amesbury,MA, makers of Dehumidification equipment states, Mold and fungus are present in almost can survive without moisture, remaining dormant for decades, even ,when moisture and a food source become available they will multiple rapidly. This moisturedoes not have to be in liquid form. Microscopic organisms can use moisture present in solidmaterials because they need so little. Two classic examples of this phenomenon are the prehistoric cave paintings in Lascaux,France, and the Egyptian artifacts preserved in the pyramids.

5 The cave paintings survivedvirtually intact for 16,000 years. Then tourists began bringing moisture into the caves in theirclothes and through their respiration. The paintings have deteriorated through microbiologicalattack in less than 40 years. Egyptian artifacts have had the same difficulty, with tragicconsequences for history. So how do we solve these humidity problems, Dehumidification of course?Many expertssay that Dehumidification is probably the most effective tool we have of controlling moisture thatcan have a serious impact on mold Palaces, Churches and Museums in Europedo not have air conditioning.

6 Thesebuildingsare full of beautiful, centuries old paintings,cloth wall murals, are stored in non-temperature controlled areas becauseof Dehumidification providing great savings in equipmentand operational can be removed from a space by several different methodsbut the one we willfocus on in this column is thecooling based Dehumidification -reheat method using a directexpansion system instead of chilled liquid for cooling the moist air enteringevaporator coil, moisturebeing removed, and drierreheated air returning tospaceCooling based Dehumidification isbasically a standardrefrigeration system with a the air is cooled at the evaporator, it is blown overthecondensing coil (reheated) and then discharged tothe space.

7 Most residential and whole housedehumidifiers use this systems operate at their highestefficiency levels provided all other variables areconstant, when the condenser air temperature is low& the cooling coil air temperature is thecondenser coilwiththecool airfrom theevaporatoris ideal since the low airtemperature makes the refrigerant condenser very reheat energy is essentially free, because it is heatrejected from the cooling process and saves on expensiveextra energy from outside the you are still wondering why we need toreheatthe air let me , warm air can hold more moisturethan cool air and moisture will move to adry object ormedia such as air.

8 Making reheated,drierair a moisture absorbing the air entering the evaporator iswarmand very moist, coupled with the leaving air dewpoint being high,cooling baseddehumidification-reheat systems operate at their peak efficiencyand are a cost effective method of dehumidifying a given House Dehumidifiers:Since Air Conditioners remove some humidity but are not designed to remove excesshumidity,you may need to use some type of supplemental humidityremovalsuch as a wholehouse whole house dehumidifier works on the cooling based reheat method and has anexpansion valve regulating the flow of refrigerant tomaximize the moisture removal underconstantly changing load whole home dehumidifiers have a 50-50 sensible to latent heat removal ratioinstead of the 80-20 sensible to latent ratio of conventional air conditionersbut unlikeconventional air conditioners that have a cooler supply temperature, the discharge air supplytemperature(supply air)

9 Of the whole house humidifierhas been reheated and can raise thesensible temperature of the space in some units can be installed as stand alone systems for dehumidifying basements&storage spaces or homes toremove excess humidity for those who canlive with the heat, just notthe humidity. They can also be tied into your conventional A/C system for extra humidity removal isnecessarybecause ofhigh humiditylevelsbutcomfort cooling is unnecessary due to lowoutsideambient temperaturescanoccur in theNortheast between May and the average dry bulbtemperaturewas less than 75 degrees and the average dew-pointwas greater than 60 degrees, a relative humidity greater than 65 % would exist making mostpeople uncomfortable.

10 The A/C would not run because the thermostatwhichsenses dry bulbtemperaturewould not be calling in most homesand humidity is a wet bulb temperature whichrequires a humidity type of situationsthat can require supplemental dehumidificationarepartial loadconditions(moisture removal of a cooling coil degrade at part load), andover sized A/Csystemsthat cool the sensible load quickly butnever really get to dehumidify the the equipmentspecifications and installation instructionsfor the specifics onapplication & installation.