GeoMass Heat Pump

GeoMass combines two building energy-management concepts: the ground-source heat pump and thermal mass. Ground-source heat pumps (sometimes called geothermal systems) leverage the constant temperature of the earth (about 55 degrees year-round at roughly 10 feet below the surface, in most locations) to make the heat pump cycle more efficient in both winter and summer. Thermal mass recognizes that some of the physical mass of a building can serve as a thermal storage to moderate temperature swings. GeoMass integrates both concepts in order to maximize benefits and reduce costs.

A ground-source heat pump installation involves drilling holes in the ground, inserting a series of long loops of pipe, and then circulates water or a refrigerant through the loops to exchange heat. The heat pump (really a reversible compressor) “pumps” heat (in summer) and cold (in winter) into the water or refrigerant. This is much more efficient than conventional electric heat (or oil and gas heat); the energy required to drive the compressor is multiplied by 2 to 4 times in heating the building. The ground-source heat pump is also more efficient than the “air-source” heat pump, which is much more common. The air-source heat pump simply pumps heat or cold into the surrounding air. The problem is that the air is hot in summer (just when you need to pump more heat into it) and cold in winter (the reverse, of course). So the air-source heat pump is least efficient when it is most needed, to the point where conventional electric heat is often needed to supplement the heat pump in many climates.

The ground-source heat pump, because it is pumping heat into a 55 degree “heat sink” (the earth underneath our feet) is uniformly efficient, year round. But the drilling is very expensive and requires specialized equipment and teams. The payback on ground-source heat pump systems can be 10 years or more at current energy prices, compared to a more conventional air-source heat pump system that doesn’t require drilling. Is there a way to get the efficiency of ground-source at the cost of air-source?

We are experimenting with the idea of using the thermal mass (and conductivity to the ground) of a building’s foundation to avoid drilling. The GeoMass concept uses a series of small (e.g. 1 ton) compressors installed in areas or individual rooms of the building. These compressors (similar in size to small window AC units) are linked through small diameter (e.g. 1 inch) water pipes to a main water loop running around the perimeter of the building, at the basement or foundation level. Each compressor heats or cools, depending on thermostats in the room. In turn, water flowing through the compressor is heated or cooled, and circulated from room to room through the main water loop. The main water loop is buried or grouted into the concrete of the foundation, and then insulation is laid over the loop. The idea is to exchange heat between the loop and the foundation, and between the foundation and the loop. Since the foundation is likely to be below ground level, and protected from outside temperature swings by walls and insulation, it is likely to be closer to the ideal 55 degree ground temperature than outside air. If there is not enough heat exchange with a simple loop around the perimeter, we can install a piping grid in part of the basement area.

There are a number of potential advantages to the GeoMass concept.

• More efficient than air-source heat pumps, particularly in summer and winter;
• Less costly than ground source, since no drilling is required.
• The system naturally balances hot and cold areas of the building, such as busy offices on the sunny side versus less busy areas on the shady side.
• The system naturally balances day and night differences in temperature and demand, by using the foundation as thermal storage.
• Many small compressors are connected through small pipes and relatively short runs to the internal loop; this makes it easier to commoditize the compressors and lower the cost of equipment and installation, as compared to more centralized systems requiring larger, more complex and specialized equipment.
• No ductwork is required, no balancing, and no centralized controls.

The GeoMass concept also integrates well with the OvalAir strategy, which uses an “air loop” to encourage thermal mixing (and ventilation) between interior spaces. Rather that ductwork and centralized HVAC systems, OvalAir uses simple fans to encourage circulation of air between rooms, corridors, stairways, ceiling spaces and public areas. This thermal mixing breaks up localized thermal peaks and valleys produced by sunlight, localized heat sources, and gravity-driven convection. OvalAir and GeoMass have similar benefits and complement each other. The result is greater comfort and lower demand at minimal equipment and installation cost;. In fact our goal with both concepts is no incremental cost over conventional systems, which means an immediate payback.