Latent Heat gain for hot showers

[Polar06]

Greetings, I am designing an HVAC system for a shower/shave facility. I have determined all the heat loads but am so far stumped on how to determine heat gained from running the showers themselves. With no guidance I am looking at doing a direct vent from the shower area to the outside environment and adding a reheat to the HVAC unit. Does anyone have a good reference or equation to find the latent heat gain from the showers, 20 in total?

Many Thanks,

 

[SAK9]

Not sure why you want to air condition the shower area when it requires exhaust ventilation.Mechanical ventilation with heating will be sufficient.If you really need to air condition it, provide a single pass system with energy recovery wheel or HEX.

 

[ChrisConley]

WARNING, the following is a mental exercise only.

Pretending (for fun) that your shower room was actually a very shallow pool of hot water with a high activity factor (due to the mixing of the showers.)

Evaporation rate of a pool=

0.1 x Area x (Vw-Vp) * Activity Factor

I'm going to assume shower water temperature of 90F (Vw = 1.422). I'm going to assume we're controlling the temperature of the shower room to 78F and 60% RH (Vp = 0.58)

Based on the above I'd guesstimate the following:

0.1 x Area x (1.422-0.58) * 1.2

0.1010 x Area = Latent Load in lb/hr. Covert to BTU/hr based on ~1000 Btu/lb.

1010 (Btu/hr)/ft2 = Latent Load at peak.

Seems reasonable, in not a little high. If the shower room can get warmer, and more humid that load will drop quickly.

Genererally, as SAK9 has pointed out, we usually use mechanical ventilation at a fairly high rate to deal with shower rooms.

 

[MintJulep]

Experimentally:

Install your shower head into a closed and sealed (except for water drain) test cell.

Also in the cell: dehumidifier, temperature and humidity measurement sensors.

Determine the ABSOLUTE humidity of the air in the cell prior to starting.

Run the shower for some representative shower-taking time.

Run the dehumidifier until the absolute humidity returns to the initial condition.

Measure the mass of water collected by the dehumidifier. Given this mass of water, the shower water temperature and the desired space air conditions you can determine the latent load.

 

[AbbyNormal]

I would neglect it, wirte it off as that is what exhaust fans are for, and worry about it on the make up air load

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

you sound like ole Ed Z gave you a dectron manual chris

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[lojack1]

I believe IMC (International Mechanical Code) requires ventilation for this application to be a 'minimum' 50 CFM per shower head (intermittent ventilation) or 20 CFM per shower head (continuous ventilation). I agree with the others, you just want to exhaust this space. So whatever makeup air you need to provide directly to this space or from a neighboring space needs to take into account the outside air provisions to fulfill this. That's your only cooling load. Btuh = (exhaust air rate, CFM) x 1.08 x (max. ambient air temp. - 75F)

 

[HVACHawaii]

lojack1. Actually that equation accounts only for the sensible load. You need to take into account latent load as well. Total load BTUH = 4.45 x CFM x delta h. Also you would want to cool down further than 75 beacause you won't do any dehumidification. I live in hot hutimd climate and we cool down to at least 55F, and then provide some sort of reheat to maintain room temperature.

 

[Polar06]

Thanks to all for the information. I have been out of pocket for awhile, but the above is exactly what I was looking for.
Thanks again