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Can someone tell whether latent load contributes to the total cooling load of a building or not.if it does, tell which way, and how it should be looked at during load calculation of a building.Also if possible display a perfect, easily understood definition of latent heat.Thanks
Any heating would count as heat load, take a look at the psychometric chart... latent heat: change the quantity of heat without change in temp, a lb of water have more heat than a lb of airQuote:
Originally Posted by Hasni
Latent heat is added with your sensible load to give you a total cooling load. ACCA well known and creditable Manual J book for residential heat load calculations defines latent heat as being heat absorbed or released when water changes to bapor or when water bapor condenses to water.
Once you know your two sides of the cooling load (sensible and latent) you have to size your air conditioner. Most think that you size it to the total load but this is a common mistake. Our air conditioners handle both loads and have a sensible to latent ratio for the cooling provided. We must look at our outdoor wet bulb temp and indoor dry bulb compared to the manufactures expanded ratings to see what percentage of the outdoor condenser specifications to see what percentage produces sensible and which provides latent cooling. We need to make sure the out door condensers capacities for each meet the capacities that the home requires for each from the Manual J calculation.
For further advice on Manual J, Manual S, or Manual D calulations please visit our website at Home
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Your HVAC friend,
Larsen Tech, Inc.
Latent heat is added with your sensible load to give you a total cooling load. ACCA well known and creditable Manual J book for residential heat load calculations defines latent heat as being heat absorbed or released when water changes to vapor or when water vapor condenses to water.
Once you know your two sides of the cooling load (sensible and latent) you have to size your air conditioner. Most think that you size it to the total load but this is a common mistake. Our air conditioners handle both loads and have a sensible to latent ratio for the cooling provided. We must look at our outdoor wet bulb temp and indoor dry bulb compared to the manufactures expanded ratings to see what percentage of the outdoor condenser specifications to see what percentage produces sensible and which provides latent cooling. We need to make sure the out door condensers capacities for each meet the capacities that the home requires for each from the Manual J calculation.
For further advice on Manual J, Manual S, or Manual D calulations please visit our website at this link Home
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Your HVAC friend,
Larsen Tech, Inc.
Latent heat does contribute to the total cooling load of a building. Your chiller capacity will be equal to the sum of latent and sensible heat (total heat)Quote:
Originally Posted by Hasni
Air is mixture of several gases but for engineering purposes we can assume that air is a perfect mixture of dry air and water vapour. Latent heat is energy required to evaporate water in to the water vapour contained in dry air- water vapour mixture.
In other words if you are adding latent heat to your space it means you are adding water to the air inside your space.
Latent heat is responsible for air humidity.
When you cool air to keep temperature in the space at certain level some of that water in air will condense so your coil has to be sized to deal with sensible heat (to reduce the air temperature) and latent heat (to reduce the water content)
Latent heat is the amount of heat that will be introduced to the cooling coil by water vapor changing into liquid on the coild surface. This change of state gives a LOT of heat to your cooling coil. The higher the relative humidity in the space, the more motor vapor will condense on the coild surface. The more condensation taking place, the less capcity the coil has for sensible cooling. (making a difference in the temperature of the air entering and leaving the cooling coil) As a unit runs for awhile, it takes a lot of the humidity out of the air, and the sensible cooling amount will increase. Latent heat is a very important part of a cooling load calculation, and equipment will have to be selected to handle your latent and sensible load. Put simply, latent heat is heat added causing a change of state with no change in temperature. Sensible heat is heat added causing a change in temperature with no change in state.
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