Systems with auxiliary electric backup or gas backup which do not require de-energizing of the compressor (split system with a DX coil in the return duct or a gas boiler assisting a water-to-water system at water temperatures below 120°F) should have a % by Geo between 96.5 – 98.5% for efficient and economical sizing.
Another method of sizing, for the above systems, is to look at the balance point and bin data. The remaining bin hours below the balance point should be between 8 - 12% for effective sizing. You can round down to the nearest bin temperature when adding up the total hours below the balance point temperature.
Dual Fuel systems which would de-energize the heat pump at a balance point can have a % by Geo as low as 80% for effective sizing of the geothermal. This decision is highly dependent upon the cost of the fossil fuel. If utilizing propane, the method of 96.5 – 98.5% will be more favorable for the operation costs incurred by the homeowner.
The heat pump’s sensible cooling capacity must always meet 100% of the sensible cooling load. If you see the red warning at the top showing, “Heat pump does not satisfy sensible cooling load at design temperatures,” you must choose a larger heat pump and check for adequate cooling capacity.
