Ventilation - Open 2nd Floor Power Plant

[ajoven]

I need to ventilate an open second floor where the temperatures can be as high as 115 F to 120 F during the summer (in PA). It is mainly unoccupied and is used for storage. Our client would like the make the 2nd floor more bearable. I was thinking of introducing outside air into the second floor using a wall power ventilator. Possibly ducting at floor level and have the air come out bottom up.

The PP has four engines and I do know the heat generated from each along with the aux. equipment. The existing ventilation is for the power house floor and has some excess capacity. The ventilation system pressurizes the power house (using power ventilators) and get exhausts out at the roof top.

The nearest engine is probably 10 to 12 ft from the area I need to ventilate. What's the best way to determine the air flow requirement (V = Q/(Density*specific heat*temp. rise))? Is Air change method better? Am I going the right direction? Any thoughts or comments would be appreciated!

Thanks in advance!

 

[CESSNA1]

AJOVEN: Having worked on the top floor of a powerplant in the summer, I can relate to that. The question is - What is the desired temperature. The lower the temperature to more outside air (presumably you will be using outside air) you will need. One way to do it is to install two sets of fans. One set to blow down from the roof and the second set to exhaust horizontally from above the engines/generators. That should set up forced convection down and out. How much depends on the desired temperature and the size of the powerplant.

Regards
Dave

 

[lilliput1]

Btu/hr heat rejected = CFM OA x 1.1 x (104 - TOA)

TOA = outdoor summer design °F wb
104°F = max rated operating temperature of typical electric equipment.

How are the engines cooled? You can reduce heat load to space using remote outdoor mounted raditors w/ glycol & insulating the exhaust pipe & muffler. Or duct radiator cooling air outside & introduce makeup air from opposite wall. Make sure radiator cooling air blows out, not in.

Introduce cold OA low to blow at occupied spaces & towards the engines. Exhaust above the engines where rejected heat rises.

 

[ajoven]

Thanks guys for your comments!

Just for clarification, the area I would like to ventilate is about 10 to 12 ft away from the nearest engine (again on the 2nd floor - 14 ft. aff). Budget is limited so doing anything to the existing engine area is probably out of the question. The engine area is already ventilated with power ventilators. The area is basically pressurized and the heat exhausts out through the roof. The roof have exhaust vents. The cooling system for the engines utilizes cooling towers.

I would like to put my efforts on the second floor area using wall fans to introduce outside air to the area. I would like to use ducting so air can be distributed to most of the floor area instead of just a localized section if not ducted and having it distribute from the floor level up. Question to CESSNA1: Why force air down from the roof since that is going to be warm air? I would say the target temperature would be 95 F during the summer if possible. The fan size and the cost may be a big factor if 95F too low. As indicated on my initial thread, what calculation method would be best (air change or CFM=Q/Dens*spec ht*temp.rise)? Is there another? And also, for an inexpensive approach, am I approaching this the right way?

Again thanks for all the comments/thoughts in advance!

 

[redgdon]

Hi,

I would agree that Q=mc(delta)T is the way to go, if you are using fresh air to try and cool the space.

What is your average summer time temperature?

If your budget will streach to installing ductwork, would an alternative solution not be to consider a DX system?

 

[CESSNA1]

AJOVEN: Perhaps I was unclear. I was suggesting that you mount roof fans that would take in outside air, which is hopefully cooler than the inside air. This ould displace the upward flowing warm air downward and then the warm ari would be exhaused out the side of the building. This way the hot air from the engine area would be exhausted and cool air from the outside would replace it.

Regards
Dave

 

[cme]

60 air changes / hour should do it

 

[HVAC68]

1. What's the ambient temperature during summer ? i.e. when your inside temperature is 115 deg F to 120 deg F, what's your outside temperature ? The thumbrule is - you can get within 5 deg C (9 deg F) of ambient temperature by introducing outside air.

2. Are you able to calculate the heat load to be dissipated ? If yes, use the Q = m Cp Delta T equation, use a 9 deg F for Delta T and find out the air quantity required. You will be only working on the sensible heat portion and hence you can use the equation,

Q = 1.08 x air quantity x Delta T

Units are in FPS

Good luck


HVAC68