Colorado Dermatology Institute (CDI), located at 1220 Lake Plaza Drive in Colorado Springs is upgrading its HVAC system for greater comfort, higher efficiency, lower operating cost and reduced carbon footprint. A new ground source heat pump (GSHP) is being installed and expected to be operational by the 1st quarter of 2019.
What is a GSHP System?
A ground source heat pump uses the earth as both a heat source for heating and a condenser for cooling. GSHP systems can provide chilled or heated air or water. For CDI, the GSHP system will be composed of forced air units.
These systems operate the same way as a conventional air conditioner, refrigerator or other heat pump operates, they merely move energy (heat).
Removing energy from air lowers the temperature of the conditioned space; this is why the air flowing off of the coils of a refrigerator is warm, since it is taking the heat from inside of the appliance and removing it through a refrigeration circuit. An air conditioner works in the same manner, it removes heat from the inside of a building and rejects it to the outdoor air through an external condensing unit. The big difference with a GSHP system is that it uses water to carry the heat to and from the building, and interacts with a ground heat exchanger (GHX) to either extract energy from the earth (heating) or reject energy back to the GHX for cooling. By using water as the energy transfer medium, and taking advantage of the earth’s greater density, mass and consistent temperature compared to outside air, a GSHP system is typically 4 to 5 times more efficient than a conventional furnace or air conditioner, never loses efficiency, nor is it derated for altitude. The same unit provides both cooling and heating, further reducing hardware, infrastructure and controls.
Each unit is referred to as a water-to-air heat pump, where the water that flows through the heat pump is the same fluid that flows through the GHX. With the heat pump, the water flows through a water-to- refrigerant heat exchanger; the refrigerant either loses heat to the water or absorbs heat depending on the thermostat setting for the zone it is conditioning. The refrigerant is moved through the refrigerant circuit of the heat pump driven by a compressor, with the heated or chilled refrigerant moving through a direct exchanger (DX) refrigerant-to-air coil that provides chilled or heated air driven by a blower.
The refrigerant is moved through the refrigerant circuit of the heat pump driven by a compressor, with the heated or chilled refrigerant moving through a direct exchanger (DX) refrigerant-to-air coil that provides chilled or heated air driven by a blower.
The GHX replaces many components in a conventional system that degrade in efficiency over time and never needs to be replaced. Equipment that is omitted includes furnaces, air conditioners, refrigeration line sets between air terminals and external condensers, condensers and related equipment are eliminated with the GHX which has no moving parts itself. GSHP systems can use a variety of earth coupled ground heat exchangers. Closed loop systems can either be drilled, excavated or trenched. For some applications where a pond or lake may be nearby, a closed loop surface water heat exchanger (SWHX) may be used. In some situations where conditions are appropriate, open loop systems may be employed using well water to service the GSHP system.
For CDI, the GHX is a closed loop system composed of twelve boreholes drilled to 500’ each, using a single 1.25” high density polyethylene (HDPE) plastic pipe assembly, with two legs connected by a u-bend at the bottom of each borehole.
Each individual borehole circuit is tied to a pair of HDPE pipes leading back to the mechanical room for connection to all of the heat pumps within the building; small circulation pumps will move water between the heat pumps and GHX. As the system is closed, the fluid within the system never needs to be replaced with reasonable maintenance.
Maintenance of GSHP Systems
Routine service of the GSHP system for CDI will consist of changing air filters on a regular basis, checking the pH quality of the water in the closed loop system once or twice a year, and a preventive maintenance check by a qualified GSHP technician once per year.
Since the GHX replaces many components typical of conventional HVAC systems, overall maintenance is vastly reduced compared to other mechanical configurations.
Due to the efficiency of the GSHP system designed for CDI the mechanical system is estimated to operate at no more then $0.50 per ft2 per year, or about $500 per 1,000 ft2 annually. This is typical for most commercial GSHP systems in Colorado.
Since a GSHP system uses a small portion of electricity compared to conventional mechanical systems to operate, even considering green house gas emissions at the point source generating the electricity, the green house gas emission (GHG) impactis negligible. As no fossil fuels are consumed by the heat pump system, there are no emissions created by the system.
The specified heat pumps use a relatively low amount of refrigerant in each unit. The refrigerant is R410a, a hydro-fluorocarbon (HFC) which does not contribute to ozone depletion. Further the refrigerant circuit is closed and sealed, and may only be serviced by a qualified, licensed technician.
Efficiency can best be explained as “what you pay for vs. what you get”. With a GSHP system, energy is only moved, not produced. For example in heating, if a heat pump is operating at 400% efficiency, it is producing 4x as much energy as that consumed. In the case of a heat pump, the only electricity consumed is that needed to operate the circulation pump, compressor and blower motor. As the system is water sourced, the compressor uses far less wattage to move energy between the water and air.