WLHP Loop with Chilled Water and Geothermal Water Sources

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I have a building that is predominantly VAV with UFAD using a boiler/chiller plant. However, one portion of the building is residential which we would like to use WLHP's for. I would like to use purchased hot water (geothermal at 110 deg from City) and the chilled water from the building plant to maintain the WLHP Loop between 60 and 90 deg.

Any ideas on how to model this?

Also, I've been a bit confused on how eQuest uses PVVT systems to represent the air-side of WLHP systems. Any references or resources anyone has that explains the theory behind this would be greatly appreciated.

Thanks,

Dan Russell, EIT

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Dan:

For your simulation, I think you can model it as a typical boiler and cooling tower system and then convert the heat rejection and heat addition loads of WLHP loop to the required energy use of the hot and cold water if you know the efficiency of the heat exchanger that isolates the WLHP loop from the hot/cold water. It may be a bit more challenging if you want to couple the chilled water system with the WLHP system. My initial thought is that you can create a dummy zone that is cooled by the chilled water system and has the internal load identical with the heat rejection load of the WLHP. You may have to run the simulation twice and manually input the internal load to the dummy zone. Why don't you use cooling tower to cool the WLHP water? Cooling tower should be cheaper to run than the chiller.

Regarding eQUEST using PVVT to represent air-side of WLHP (water-to-air heat pump), the reason is PVVT has more flexibility to model packaged DX coil unit. By specifying stages of cooling and heating capacity, minimum airflow ratio, and applying proper performance curves, PVVT can model either conventional heat pump with single stage compressor and constant speed fan, or more advanced heat pump with two-stage compressor and variable speed fan. In addition, with PVVT, you can simulate a DOAS that heats and/or cools the OA with a water-to-air heat pump after OA is preconditioned with ERV.

Hope it helps,

Xiaobing

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My understanding is that if you assign multiple zones to a PVVT, it is
modeled as a single central water-cooled DX cooling/heating coil serving
multiple zones. One zone is designated as the control zone and the
central coil is controlled based on its thermostat.

According to the DOE2.2 help file:

"The airflow to all other zones is proportionate to the airflow of the
control zone. In other words, the thermostats in the non-control zones
have no effect on either airflow or supply air temperature. They may,
however, modulate a reheat coil or baseboard."

Thus, there may be times where there is simultaneous cooling and heating
for some zones. The only way to have one compressor per zone is to
assign each zone to its own SYSTEM.

For the HP system type, when multiple zones are assigned to a single
SYSTEM, each zone is modeled as having its own compressor and DX
heating/cooling coil. This eliminates simultaneous heating and cooling.

This is all based on my review of the DOE2.2 help file. If anyone has a
different experience, I would appreciate hearing about it.

Thanks,

Doug Maddox

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Doug:

You made a good point regarding the zoning of PVVT system. In fact, when simulate a WLHP or GSHP system, eQUEST will assign PVVT system to each zone. So that, the temperature and/or humidity of each zone can be individually controlled by the assigned PVVT system. In addition, heat recovery between zones with simultaneous heating an cooling needs can be accounted for in the WLHP/GSHP loop temperature calculation.

In the Design Development wizard of eQUEST, user can select zoning method for PVVT from the four options: System per Zone; System per Floor; System per Shell; and System per Site. However, it is recommended to use "System per Zone" for simulating WLHP or GSHP system (which uses multiple water-to-air heat pumps to independently cool/heat each individual zone and recover heat among zones when simultaneous heating and cooling occurs among the conditioned zones). Using other zoning method, may result in under cooled/under heated hours due to the reason explained by Doug in his following message.

Xiaobing

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