We are working on a residential project in climate zone 4A served by water loop heat pump system for heating and cooling. The baseline system is PTAC with fans running continuously throughout the year and compressor cycling based on heating and cooling load.

In the proposed case, the operation of the compressor and fan are controlled by cooling and heating load i.e. the compressor and fans will be off when heating/ cooling is not required. Additionally, the fresh air intake is through the unit's HVAC system.

According to G3.1 #4 Schedules "Schedules for HVAC fans that provide outdoor air for ventilation shall run continuously whenever spaces are occupied and shall be cycled on and off to meet heating and cooling loads during unoccupied hours."

Due to intermittent operation of unit's HVAC system, the fan equivalent full load hours (EFLH) are much lower than the baseline case. The schedules for HVAC fans are identical in both the baseline and proposed case.

To meet the ventilation requirement in the residential units when HVAC system is not operating during occupied hours. Can we demonstrate ventilation through suction of toilet exhaust and operable windows. We have exhaust fans in toilets of each residential units which will run continuously. As per EnergyStar Multifamily high-rise program, the continuously operating exhaust fans that pulls fresh air through any opening meet the requirement of "HVAC fan schedule" section.

Will this suffice the requirement of ventilation provision and ASHRAE modelling protocol for LEED EAp2 and c1?

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Mon, 11/12/2018 - 17:41

Can you meet the ventilation requirements with the exhaust fan/operable windows alone? There are limitations to this method such as distance to windows and size of operable area. If so then the ventilation should be based on natural ventilation in both models and the fans should cycle in both models. If not then the ventilation through the unit's system must run continuously to meet the ventilation requirements. The only reason you would have significantly different EFLH is is there was a separate system from the water loop heat pumps bringing outdoor air to the units in the Proposed case.

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Tue, 11/13/2018 - 14:06

1) The outdoor air supply for both models should be the same (whether the said fresh air is from a mechanical system or from "windows"...unless you can more accurately simulate natural window ventilation, in which case the availability of those systems and the controlers, whether simulated humans or automated systems shall have the same criteria for acutating the windows). 2) Heating and Cooling shall cycle to meet the load. 3) The availibilty schedules of equipment should be the same in both models. In your case is not black or white but I would consider that definately the toilet exhaust defines the min. fresh air rate (the make up air comes ultimately from outdoors). Everything over and above that I would consider part of your heating/cooling system (whether that is an efficient system or not).

Gurneet Singh

Director

Environmental Design Solutions Pvt. Ltd.

LEEDuser Expert

13 thumbs up

Tue, 12/11/2018 - 11:39

Thank you Marcus and Jean. We have also raised the query to GBCI and response is below: "Your understanding of the Baseline Case system type 1/2 fan operation (providing ventilation air and runs continuously during occupied hours) and the Proposed case fan operation (run based on thermostat) is correct. Generally, we can see fan energy usage savings due to this setup. I would recommend you to study Multifamily Energy Model Simulation Guidelines (https://www.usgbc.org/node/9462224?view=resources&return=) which provides detailed guidance on how to simulate this type of project. The guide is noted under EAp Minimum Energy Performance Further Explanation Section in credit library. I also want to bring your close attention to EQp Min. Indoor Air quality requirements. Please note that ASHRAE 62.1 does not allow operable window to be used as a mechanical ventilation air intake as it can be closed. As such, when the heat pump is off, using the restroom exhaust fan and the operable window for provide ventilation for each apartment is not allowed. However, based on LI 10416 and addendums to 62.1-2013 and 62.2-2013, it is allowed to use 62.2-2013 documenting this prerequisite in-unit compliance and using 62.1-2013 documenting non-unit compliance. 62.2-2013 defines operable window as one type of ventilation air openings." well, I am going to study in detail the Multifamily Energy Model Simulation Guidelines for EAp2 compliance and will post if there are significant variation from Appendix G for multifamily project. Thank you.

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Wed, 12/12/2018 - 09:58

"Please note that ASHRAE 62.1 does not allow operable window to be used as a mechanical ventilation air intake as it can be closed." - The makeup air need not come through the windows. If the heat pump damper does not close when it's off, you have a direct ducted connection to outdoors. And leakage rates of windows are a thing. I guess it really depends. I just renovated a hotel that has only a 60 m³/h exhaust in the toilet. It's an old envelope and the makeup air comes from closed windows as much as anywhere else (under the door from the corridor that in turn is connected to the stairwells which also have windows, etc.) This is not LEED standard by any means, but it works. This is one of those times where you may need to consider the compliance of 62.2 and 90.1 wholly seperately although they are tightly entwined.

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