Someone sent you ASHRAE. For a cold weather pool I calculate I calculate the maximum stack for the space and try to keep the high point zero or slightly negative.
I like to use active pressure control, so the infiltration will vary with temperature, but sometimes I have static fans so the infiltration is fairly constant.
Exactly how much flow is required to maintain pressure control depends on the building wall area and height. I have had pools leak as much as 1.5 cfm/sq ft or more (pardon my IP thoughts), but even a US army 0.25 cfm.sq ft air tightness could leak more than
the ventilation air requirements of a typical pool. I have tested a museum we designed at just under 0.1 cfm/sq ft so better air tightness is possible. These leakage rates are measured at 75 Pa pressure. The formula is leakage = C * Pa^n. n=0.65 is a fair
estimate so you can calculate C. Now the pressure in a cold climate will vary linear with height and should be zero or slightly negative at the roof. A problem with pools is that the exterior roof and walls may be fairly air tight, but the pool is not properly
sealed off for adjacent interior spaces. When that happens you can’t get pressure control and you often humidify the adjacent spaces to some detrimental condition.
What often happens is the normal stack pressure in a space will make a slight negative at the pool deck, and everybody goes “great, we’re done”. However if
you calculate the room stack pressure for inside and outside temperature, you find that there is positive pressure part way up the wall to the roof. Worse is when you turn off the mechanical system and the room becomes more negative at the pool deck. So
now you have some tools that allow you to estimate infiltration. I know, you would like to enter 0.25 cfm/sq ft somewhere and have EnergyPlus do the work. Sorry, not yet, but I could think of a way to make the AirFlowNetwork do some of the heavy lifting.
Do not confuse ACH recommendations with fresh air ventilation. The 4 ACH pool recommendation is simply the volume of air circulation in the space. Generally
if you move that much air you should have well mixed ventilation, but not always. The only time you would have 4 ACH of 100% outdoor air is when you have a system using fresh air for dehumidification. Some systems with air-to-air heat use fresh air for dehumidification,
but usually they need 6-8 ACH for good control. A portion of that air needs to be fresh outdoor ventilation air, usually about 0.5 cfm/sq ft of pool water and pool deck(may be a little less with latest ASHRAE 62) plus additional air for occupants if needed
(typically only for pools with audience areas, though small pools with large decks could have ventilation driven by occupancy). Often there is pressure to stop ventilation completely during unoccupied times, but the uncovered pool water still emits things
that should be diluted by ventilation, so my lowest ventilation limit is by pool water surface area.
Ned Lyon, P.E. (MA, WV)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
617.285.2162 mobile
781.907.9009 fax
www.sgh.com
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Tuesday, December 09, 2014 7:57 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] Pools application
Great information, Ned.
I'd like to ask a few questions regarding your last paragraph:
- Do you know what is, or where I can find, the recommended negative pressure in swimming pools?
- When you said that at this recommended pressure, infiltration would be 1-2 times the required fresh air ventilation, do you mean that infiltration alone would be 4-8 ACH (1-2 times the 4 ACH recommended by ASHRAE)?
- As long as I understood, you say that most pools don't have in fact negative pressure. Do you have then any idea of what infiltration normally is in common swimming pools?
Thanks,
Rui
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Posted by: "Edward G. Lyon" <EGLyon@xxxxxxx>
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