A GCHP system is one of the most energy efficient ways to heat and cool a building…almost any building. Homes, schools, offices, churches, stores…almost any kind of building, almost anywhere in the world. There’s even a system in Anadyr, Russia (Siberia) that extracts heat from the permafrost under the building to ensure the permafrost stays frozen.
There are some market barriers that have prevented this industry from growing even faster than it has been:
Initial cost to build the system is higher than a conventional HVAC system…mainly because of the cost of building the GHX
Mechanical system designers are not comfortable with the design of the energy source…the pipe buried in the ground
Even with the market barriers, more and more systems are being built. Increasing energy costs, greater concern about the environmental impact of buildings, government policies, green building initiatives and increasing pressure from clients have put more pressure on building design teams to provide their clients with better information about the cost of installing energy efficient space conditioning systems and the cost of energy to run them.
Ground coupled heat pump (GCHP) systems, also known as geothermal heat pumps, earth energy systems, GeoExchange systems, ground source heat pumps, etc., are being demanded by more and more clients, and more architectural and engineering firms are having to design the systems and the ground heat exchangers that provide the heat source and heat sink for them.
In many ways the design of a GCHP system is no different than designing a conventional HVAC system. The equipment inside the building is not significantly different than the equipment used in a conventional HVAC system. The distribution system is much the same as the distribution system of a conventional HVAC system. The only significant difference from a conventional HVAC system is the temperature of the hot water delivered by a central water to water heat pump system as compared to a conventional gas boiler. Heat pumps can’t typically supply water to temperatures greater than about 120 deg F…gas boilers offer supply hot water at 140 to 180 deg. F.
There is one significant difference, however, in the energy source and heat sink of a GCHP system when compared to a conventional HVAC system. For all intents and purposes, a conventional system is connected to an energy grid, or fuel is delivered when needed to the building. Someone, somewhere else is responsible for delivering energy to the building. Engineers and service workers at the gas company work hard to ensure the gas line to a city is large enough to supply gas to all the buildings in a city to meet the heating demand on the design day. They ensure enough gas is available from the gas wells and storage systems to make sure there is gas flowing through the pipelines. Same with the electric companies. The oil companies as well work hard to ensure there is enough oil available to deliver to their clients. For all intents and purposes, the energy supply is infinite as long as the bills are paid.
The engineer designing a conventional HVAC system doesn’t have to concern him or herself with the energy source, other than to ensure it can deliver enough energy on the design day.
An engineer designing a GCHP system, however, is not connected to an infinite energy source. He or she is connecting the HVAC system to a finite mass of dirt and rock that only deliver and absorb a relatively finite amount of energy.
This introductory video describes how energy modeling can be used to optimize the design of a GCHP system…how it can affect the cost of installing a GCHP system as well as how it can impact the efficiency of the system.
This video is an introduction to the role of energy modeling in designing a GCHP system.