[Equest-users] Ventilation in Multi-Family Building

[Nathan Miller via Equest-users]

We model this type of building regularly for Seattle, WA projects. In our mild climates it is typical that there is a dedicated make-up air path for the continuously running whole house fan. We most often see trickle vents integrated into the window frames (again, mild climate, so introducing 30-50 CFM of ambient-temp air directly into the space is not considered poor-form).

In our model we run the whole-house-fan continuously, and model it as bringing in infiltration air, so the space conditioning system see’s the load from the vent air. Then we allow the space conditioning system to cycle to meet the load in the space (which is ventilation dominated, but also includes envelope, occupant, equipment, and lighting loads). You can modify the schedule if you want to represent some additional intermittently operating exhaust fans (such as kitchen ranges, laundry closets, or secondary bath fans) IF you believe the make-up-air source will be more outside air.

[cid:image001.png at 01D1B72D.5906BC40]

To my knowledge most codes do not allow for the corridor pressurization air to be considered the make-up air source for the whole-house-fan (unless the air is directly ducted to the apartment units). But if the source of the make up air is essentially from a DOAS unit, I probably wouldn’t model anything in the individual zones (presuming they are more or less receiving neutral air), and the ventilation load will be met by the DOAS system. The zonal system again would just cycle to meet the conditioning needs of the space.

Regarding the baseline system, it is a little contentious how much “credit” we should receive for whole-house-fan systems (which for their many drawbacks, do tend to be low-fan energy). By my reading of Appendix G (and backed up by numerous LEED reviewed and approved submittals), the baseline HVAC systems are intended to provide BOTH conditioning AND ventilation. PTAC/PTHP are constant volume, with the fan sized to meet the space conditioning load. So we model the PTAC fan as running continuously, and zero out the exhaust fan kW/CFM (because all system fan energy is assigned to the HVAC unit). Typically we leave the other inputs the same for the OA exhaust scheme. This is based on noticing that if you switch to using the OA inputs for the baseline case (and not the exhaust air inputs) eQUEST tends to calculate a very different OA load in the space, even if the CFM is identical. We were never able to justify this, so we’ve stuck to modeling the OA flow same-same in the BL and PROP.

Hope this helps.

Nathan Miller, PE, LEED AP BD+C – Mechanical Engineer/Senior Energy Analyst
RUSHING | D 206-788-4577 | O 206-285-7100
www.rushingco.com<http://www.rushingco.com/>

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Sunayana Jain via Equest-users
Sent: Wednesday, May 25, 2016 6:10 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Ventilation in Multi-Family Building

Hello,

I have 12 storey multi-family building in PA. Corridors are served by Makeup Air units with high CFM (0.9 CFM/sq.ft). Apartment units are served by split fan coil units (dX cooling and hot water boiler). Apartment bathrooms have continuously running exhaust fans of 30 CFM each.

How will be apartment ventilation modeled for proposed case?

1)      Will it be assumed that Outside Air is coming through infiltration?

2)      Do I need to put Outdoor Air flow value for apartments in eQUEST manually? Would this value be zero since apartments are naturally ventilated?

3)      Should I take supply fan on cycling for fan coil units?

4)      What would be the source of exhaust for the bathroom? Would it be infiltration or air handler?
How will be the apartment ventilation modeled in the baseline case?

1)      Baseline system would be PTAC for apartments. Since Outside Air will be provided through PTAC, should the supply fans be set for continuous operation?
As I understand that this is pretty common situation in multi-family buildings. I am interested in knowing that how other energy modelers work on this scenario.

Thanks,

Sunayana
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