One unique capability of the GxTracker™ is to accurately document both the energy produced by a GSHP system as well as the energy consumed. Combining this system-level performance data with local fuel costs, we can calculate the actual cost saving realized by the GSHP system.
STEP 1.
Compute GeoExchange: One-minute resolution ground loop flow rate and temperature data enable the calculation of the amount of thermal energy exchanged with the ground.
STEP 2.
Compute GSHP Operating Costs: The operating costs are calculated from the total kWh consumed by the Compressor and Loop Pump. GES uses two options for computing these total kWh. Option 1 is to use measured kWh values for the Compressor and Loop Pump with the GxTracker™ Power Accessory. Option 2 is to use modeled kWh values based on heat pump manufacturer specifications for the heat generated by the compressor (these compare very well with measured values). The kWh for the loop pump is modeled using ASHRAE and AHRI pump penalty models for closed and open loop systems, respectively. Total kWh is multiplied by local electrical rates that are either input by the end-user or obtained from US DoE Short Term Energy Outlook for GSHP location. Caveat: The current analysis does not include Hot Water Generation, these measurements and calculations are currently under development.
STEP 3.
Account for GSHP Compressor BTUs: Electrical consumption of the heat pump compressor is converted to thermal energy. In Heating mode, this energy is added to GeoExchange delivered to the building. In Cooling mode, this energy is added to the thermal energy rejected from the building and is sent to the ground loop.
STEP 4.
Compute Conventional Fuel Cost: The conventional cost to achieve the GSHP Heating (GeoExchange + Heat Pump BTUs) or Cooling (GeoExchange – Heat Pump BTUs) is computed using equivalent fuel costs.
Results to Date
From mid-March through early July, the GxTracker™ installations in the Seacoast Region of New Hampshire show significant cost savings. It is interesting to note that the installations that are newer (and have multi-stage compressors) are also the ones that show the largest cost savings. Go to Live Sites to learn more about these installations.
