calculation of a 100% outside air cooling load 3

[pablo2410]

Hello, I´m new in this forum and have a question.
I need to calculate de cooling load of an area that demands 100% outside air, and to be honest, I don´t Know how to do it. There are some questions that comes to my mind: What should be the leaving air temperature? The loads produce by people, lights, walls, etc that we estimate in a recirculating system, should be calculated in this kind of system too?. I really apreciate some help. (I´m from Dominican Republic, so excuse my english).

Thanks.

 

[sloyal]

Here's my 2 cents...

BTUH = 4.5 x cfm x Delta H
H=psych chart enthalpy
McQuay & Trane as well as others have downloadable Charts that should give Enthalpy conditions,
I prefer the straight edge on a paper graph (calcs for the files)

My design conditions are 89db/73wb Enthalpy = 36.5
indoor cond. 75dF 50% Humidity Enthalpy = 28.0
or 70dF 50% Humidity Enthalpy = 26.3
For ease of use I call it a dH of 10

Btuh= cfm x 4.5 x 10

If I find I need a 20 Ton system, I'll be very careful to select a coil on face velocity, to avoid freeze up,
as well as Latent & sensible capacities.
Interlaced coils with multiple stages (more is better) work best.

I avoid conditioning the space with this system as it would require a larger system.
I prefer delivering room temp air & having a seperate recirculating system for space loads. I may even deliver a portion of the "tempered outdoor air" into the return of the space conditioning system, Possibly 100% if the cfm matches, with a return setup for independent operation.

My winter design is -20dF so any outdoor air is heated & it's usually done with a direct fire MAU. The products of combustion in this air has recently become an issue, especially on units recirculating any inside air.

With these design conditions, I would look at incorporating a Heat Recovery Ventilator. Something like a RenewAire with latent & sensible exchange can save a boatload on the aforementioned Gas MUA w/20ton coil.
Exh air conditions (i.e. dust, oil, etc...) might prohibit a heat exchanger altogether.

good luck
slj

 

[Yorkman]

One thing not to overlook is that the latent load is going to be rather high, given that this is a locker room with showers. A recirculated system's latent loads at the coil could be higher than the OSA senario. I would look up latent load and air change recommendations in the ASHRAE Fundamentals Handbook. It may make more economical sense to go with 100% O.S.A. and keep my discharge air at say 60 65 degrees afterall it is a locker room. Hey I have enough problem with shrinkage. ;>) Good luck, with this much advise how could you go wrong?

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int.

 

[CoreTech01]

Quote________________
ok, here is the problem

a locker room
Area 3550 sqft
height 10ft
35 persons in the room
what will be the diference in my load calculation if the system is 100% recirculate air or 100% outside air.
_____________________

The difference in your load calculation is HUGE.

Post a little more information like what’s your design room temp? For public locker rooms I design around a 77-78 Deg. Indoor temp year round.

A few things you need to know first about locker rooms.

Locker rooms should always be kept slightly negative.
The locker room area should be completely sealed NO plenum returns No mixing of air with other systems.
You are allowed to re-circulate air providing it is the air from the locker room area.
You must have exhaust fans.
You don’t always need 100% Outside air just enough to provide proper ventilation to match your exhaust.

I have use E.R.V’s in locker rooms to recover as much energy as possible to lower the load.

In your case if you use 100% outside air you will need to exhaust 110% of that air (to keep the space slightly negative)
That’s a HUGE load to cool and then to exhaust if you live in a warm climate.

Core