Requirement Summary
If the project includes ground source heat pumps, the actual COP (coefficient of performance) of the system must be entered in the software (even if the COP is lower than the base case). The COP is used to establish the efficiency. Savings can be achieved if the Ground Source Heat Pump system achieves a COP greater than the base case, as set out in the Key Assumptions for the Base Case in the Design section.
Intention
Ground source heat pumps (GSHPs), sometimes referred to as geothermal heat pumps (GHPs), are used to heat and cool buildings by absorbing naturally existing heat from the earth. A GSHP/GHP takes advantage of the more constant below-ground temperature within the earth (soil or water) compared to the more variable outside air temperature. Below-ground temperature is warmer than the air during the winter and cooler than the air in the summer. A GHP takes advantage of this by exchanging heat with the earth through a ground heat exchanger. A GHP can reach a high COP of 3 to 5.2 on the coldest winter nights, compared to air-source heat pumps that only reach up to a 1.5 to 2.5 COP on cool days. Ground source heat pumps are a clean alternative utilizing renewable and reliable sources of energy.
Approach/Methodologies
EDGE uses the Coefficient of Performance (COP) to measure the efficiency of the ground source heat pump. As defined in ASHRAE, the COP is the “ratio of the rate of heat delivered to the rate of energy input, in consistent units, for a complete heat pump system, including the compressor and, if applicable, auxiliary heat, under designated operating conditions.” For consistency, the ARI conditions should be used for comparison of COP values.
To achieve savings from this measure, the Ground Source Heat Pump must have a COP greater than the base case. The COP for an efficient ground source heat pump ranges between 3.6 and 5.2.
If air conditioning is not specified, any cooling load will be displayed as “virtual energy.”
Potential Technologies/Strategies
Four major types of ground source heat pump systems (GHPs) are available. Of these four types, three systems – the horizontal, vertical, and pond systems – are closed loop systems. The fourth major type of GHP is the open loop system. A closed loop system recirculates antifreeze or water through a loop of piping that is either buried in the ground or submerged under water. A heat exchanger transfers heat between the refrigerant in the heat pump and the antifreeze/water solution. An open loop GHP system pumps water from a ground or water source, circulates the water and then discharges it once the heat has been transferred into or out of the water. It draws fresh water instead of recirculating the same water again.
Table 38: Types of Ground Source Heat Pumps
| System | Geothermal Heat Pump Type | Process |
| Closed Loop System | Horizontal | A horizontal closed loop is usually the most cost effective for buildings with adequate land space available, in which trenches are easy to dig. This type of installation is composed of pipes that run horizontally in the ground. A slinky method is sometimes used to loop or coil the pipes along the bottom of a wide trench if space is inadequate space for a true straight horizontal system. Essentially, coiled loops are more economically and space-efficient. |
| Closed Loop System | Vertical | A vertical closed loop installation is usually most cost-effective for building sites with limited amount of land space or where existing landscape is to be preserved. This type of installation is composed of pipes that run vertically beneath the ground. Holes are drilled into the ground, in which each hole contains a single loop of pipe that ranges from 30 to 100 meters deep. Vertical pipes are then inserted and connected to a heat pump within the building. This type is more expensive to install due to the drilling, but less material (piping) and land are required. |
| Closed Loop System | Pond/Lake | A pond or lake closed loop system is used only if a body of water at least 2.5-meter-deep body is in close proximity to the building property. A supply line pipe runs underground from the building and connects to large, coiled pipes that are located deep beneath the water. Due to advantages of water-to-water heat transfer, a pond system is both a highly economical and efficient option for a heat pump. |
| Open Loop System | Open Geothermal Loop System | An open geothermal loop system uses a well or pond to pump fresh water into and back out of the geothermal system. The water is used as the heat exchange fluid that circulates within the GHP. An abundant source of fresh clean water and a water runoff area is essential for a successful open loop system. |
Relationship to Other Measures
The local climate, heat gains and the internal temperatures based on the building design impact the cooling load. A more efficient system will not impact other measures, but several measures will impact the total energy use of the cooling system.
When a ground source heat pump is selected as an energy efficiency measure, the heating and/or cooling energy is reduced depending on the load on the building systems. The energy use by pumps is slightly increased due to the operation of the system.
Assumptions
The base case includes an air conditioning system based on ASHRAE 90.1-2007, which is typically a Packaged Terminal Air Conditioner (PTAC) (a ground source heat pump is not a default base case system). The efficiency (COP) value of the base case in EDGE varies depending on factors such as building area and location. The improved case COP for the ground source heat pump system varies between 3.6 and 5.2 depending on the location; if the system efficiency is different than the default value provided in EDGE, then the actual COP must be entered.
Compliance Guidance
To demonstrate compliance, the design team must describe the specified system and provide documentation to support the claims.
| Design Stage | Post-Construction Stage |
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At the design stage, the following must be used to demonstrate compliance:
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At the post-construction stage, the following must be used to demonstrate compliance:
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