GSHP EIR Part Load Curve

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SIM List,

We are modeling a GSHP system in eQuest. After selecting the options in the
wizard and running the model we noticed that the space heating was quite a
bit lower when compared to a VAV system for the same project.

We then went into detailed mode and started to look into what performance
curves the heat pumps had defaulted. It seemed that the default part load
curve (HEAT-EIR-FPLR) that eQuest selected, seemed very aggressive. It is
my understanding that the heat pumps cycle on and off when needed, and when
they cycle on and off they operate at 100%. So, should the part load curve
be changed to be 100%, (ie it shouldn't have a part load curve)? Or should
we be looking at something else.

Thanks,

Tony Kriel

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The simulation time step in DOE2 is 1 hour and heat pumps won't run all
the hour if you are in part load conditions; so they don't operate at
100 %.

As during the hour, they cycle many times, there are losses and you need
the curve HEAT-EIR-FPLR for that.

______________

Demba Ndiaye

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Reputation: 200

Two things could be throwing off your comparison.

Not knowing what your baseline heating system is, the ground source heat pump will have a lower heating energy usage compared to conventional systems at the building line (electricity used at some COP compared to 80%-90% boiler/furnace or electric resistance heat at 100%). Relative costs of each depending on your location.

Also the VAV system may have reheat where the zonal system will only be providing heat to meet the loads.

David

David S Eldridge's picture
Joined: 2011-09-30
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Also, several manufacturers have started using dual stage compressors giving
them part load ability.

Anthony Hardman

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Usually when you specify a heat pump system, the cooling compressor type is
specified as single speed (under airside HVAC, Cooling, Unitary Power). I
believe that the part load ratio is based on how often the compressor cycles
over the hour simulated.

Also, even though the system is PVVT, default minimum airflows are given at
a ratio of 1.

--
Karen

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Joined: 2011-09-30
Reputation: 200

The simulation time step in DOE2 is 1 hour and heat pumps won't run all
the hour if you are in part load conditions; so they don't operate at
100 %.

As during the hour, they cycle many times, there are losses and you need
the curve HEAT-EIR-FPLR for that.

______________

Demba Ndiaye

Demba Ndiaye's picture
Offline
Joined: 2011-09-30
Reputation: 200