[Equest-users] Modeling HVAC system with heat recovery

[Haberl, Jeff]

Hello Ahmad:

When considering air-source heat pumps you also need to carefully in cold climates to watch for large peak heating demand since the heat pump simulation in PSZ will switch-over to electric resistance heating as temperatures below apx. 30F. This results in a large jump in electric demand as the unit cannot maintain space temperatures at outdoor temperatures below 30F.

This was one of the reasons for the large, unexpected load on the grid during the winter storm a few years back because of the large number of Texas residences with air to air heat pumps.

Avoiding this is possible with a ground heat exchanger for the heat pump (if this is possible on the site).

Also, several manufacturers are solving this with new technologies that allow the heat pump to continue to provide heat in cold climate conditions. However, defining these new HP systems in DOE-2, Equest or EP+ requires some work with adjusting the equipment parameters.

Jeff


Jeff S. Haberl, Ph.D., P.E.inactive, FASHRAE, FIBPSA               We are like fluttering leaves on the branches of trees

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________________________________
From: Equest-users <equest-users-bounces at lists.onebuilding.org> on behalf of Brian Fountain via Equest-users <equest-users at lists.onebuilding.org>
Sent: Monday, September 4, 2023 5:55 AM
To: Ahmad Fraij <fraij at yahoo.com>
Cc: equest-users at onebuilding.org <equest-users at onebuilding.org>
Subject: Re: [Equest-users] Modeling HVAC system with heat recovery

You have a couple of options regarding system type. There is a HP heat pump system type that is zonal meaning you would not need a system per zone.    However it has some keyword limitations including no ventilation heat recovery.    So to work
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You have a couple of options regarding system type. There is a HP heat pump system type that is zonal meaning you would not need a system per zone.   However it has some keyword limitations including no ventilation heat recovery.   So to work around model heat recovery you will scale back the OA volume by the heat recovery effectiveness.   ( Not terrific. )

I recommend creating a system per zone and using the PVVT system type. PSZ would also work.  PVVT enables a few more keywords.   Both allow ventilation heat recovery to be directly modelled.

Whichever system you choose, set your heating to Heat Pump.   The keywords on the heating-supplementary tab will be enabled where you can add the OAT below which your electric resistance heating is enabled (default 40F) and the OAT below which the heat pump doesn't run.
On Sep 4, 2023, at 12:38 AM, fraij via Equest-users <equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>> wrote:
Hello,

I have a model in eQUEST that has FCU as the HVAC system with heat pump chiller for a residential building.

Now I need to change this HVAC system to DX heat pump and this heat pump is small and self contained in which it can be installed inside the room and will have inlet and out let ducts for the condenser air to the outside (I.e. without outdoor unit). This unit will have also heat recovery option and supplementary electric resistance heater.

My question is, what is the best HVAC system in eQUEST that I can use for this heat pump and in the same time enable the heat recovery option tab and the supplementary heater option tab? And also, do I need to assign a new HVAC system for each zone or I can assign one HVAC system for a group of zones similar to the FCU system?

Thank you very much for the help.

Regards

Ahmad




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