3 story apartment design

[DuctHunter]

OK guys, I need some advice. I am designing a 3 story apartment building. Per the owners request we will have condensing boilers to heat the aparments via hot water fin tube. Cooling will be done with a "thru-the-window" AC unit. Each apartment has a local toilet exhaust fan interlocked with lights and a kitchen exhaust hood. So exhaust will be intermittent.

My questions are if I will be supplying 100% OA make-up air (DX cooling for tempering) with some diversity factor into the corridor for the toilet and kitchen exhaust.

1) Is it better to go with gas fired MAU units or Hot water to take advantage of the high efficiency boilers.

2) if the make-up air unit is supplying all three floors how would you control it for building pressure.

3) Is it better control wise to have 1 MAU per floor thus increasing the first cost ( 3 MAU's and 3 Condensing units)
or 1 MAU for the building, but how would it be controlled.

Thanks for your help.

 

[MintJulep]

How are utilities billed?

If heat is included in the rent then use the boilers. If tenants are paying for heat then you'll need a separately metered supply for the common areas.

 

[DuctHunter]

If I go with hot water make-up air units. Will I need to provide a face and bypass damper. Is freezing the coil going to be an issue ?

 

[Drazen]

Just general thought - it could be hard or impossible to find air heating unit that works in low temperature regime.

Of course, you can set your condensing boiler temperature higher, but than it is useless to have condensing feature at all.

Freezing is an issue if your outside design tempereture is low.

 

[cdxx139]

iS there an emergency generator?

If so, add a freeze pump, a small recirculating pump for the hw coil that runs when oa is below 40.

If not, add glycol, for freeze protection.

knowledge is power

 

[ChrisConley]

You can use low temperature boiler water to heat air from even extremely low outdoor temperatures. It requires a much deeper coil, which adds cost and pressure drop to the system. I have now used a commercial condensing gas-fired MUA. A little on the pricey side, but payback is reasonable.

You can't really use low temp water for fin tube though. Once the fin tube stops convecting, it stops working. I saw a presentation on using a _large_ deltaT on fin tube for condensing applications (180F/100F).

On the MUA side, no reason not to use a variable speed fan with pressure control in each corridor. Variable speed would favour hot water coil, but most gas-fired heat exchangers now support variable air volume.

 

[317069]

Hello
1- I think it would be better to separate between the apartment heating system and make up air system because of operation schedule, maintenance ...etc
but about which is better boiler or MAU, you have to check the cost and energy consumption in both cases.
2- it depend on the area of each floor, if it was too large then you could devid building vertically to save duct work.
if it is small you better use on unit, don't worry too much about pressure, it is an apartment building, doors will be always opened, just you have to choose enough cfm.