Humidity Calculation

If you warm the room air from 21C to the max allowable (24C) your relative humidity will go from 66% to 55.03%. It's cutting it close. You might consider dehumidification. These numbers were calculated using the Magnus-Tetens approximation (1974).

Dear Sir,

Please check your heat load estimation form particularly the internal load. While estimating the heat load the consultant must have assumed some equipment load which dissipates sensible heat. Based on the calculation the designer must have selected the ADP9 Apparatus dew point temperature) of the coil and the AHU. Check the calculations with the help of P_s chart and take action appropriately. You can always use heaters to dehumidify it. Plot these process in P-S chart, get the values and use simple formula to arrive the capacity of the heater.

Regards,Dr.Rams

It seems that your installation is designed with cooling in mind only. You did not mention if there was any humidity control device (Dehumidifier or Humidifier).

If the above is correct, the Only control available for the humidity in the room is the cooling coil of your AHU: It cools the air therefore removes some of the water (condensation) ---> is dehumidifying automatically. It does not add humidity and is OK for the pupose.

You are achieving 66% RH from but from what level? HERE you should look at the fresh air input volume and its RH% to see how much water you have removed in the AHU!

If the RH% of the outside air is high you need to either reduce the fresh air intake so that you can achieve the 55% or add a dehumidifier unit before the AHU fresh air (or even on the return air duct to the AHU... depends on the duct work etc.)

re-frsh your knowledge on the Air Humidity Chart and how to work with it (Psychometric chart). It needs some concentration to remember the mechanism of Water in the Air ...etc

The heater should be sized to offset the heat loss which you will have to calculate, based on the construction of the structure. The 2009 ASHRAE Fundamentals handbook can guide you through that calculation. Lou Bindner

I would install a 3KW electric heater coil and connect to a humidistat control. The heater will reheat the air and allow the cooling coil to continue condensing water out, while NOT over cooling. This will allow you to set the humidity to what you want it, say 50%. Be advised that the energy cost will go up.