GEOTHERMAL: WHICH BUILDING SIZE IS BEST SUITED, LARGE OR SMALL?

We've been asked if there is a building or home size that's better suited for geothermal applications. The answer is ... not really ... or perhaps better stated ... it shouldn't matter.  If a building, regardless of size, is well constructed and insulated, a well-designed geothermal system is the best choice above all others for long-life and lower operating costs.

Multiple Government Buildings on Large Closed Loop System

Building size is not the concern; rather it's the quality of the building materials, including insulation quality and tightness, and how these items impact the amount of energy necessary to satisfy heating and cooling demands - i.e. impact on the ability to maintain internal room temperatures in the context of heat loss in winter and heat gain in warmer months. 

                                                       

7000sqft Norwell Home with Natatorium (Pool)

 

This more important consideration, building material quality, directly impacts the required size of the geothermal system and therefore the initial and recurring operating costs.  To minimize these costs, the owner should first invest in minimizing heat loss and heat gain.  It can easily be shown how the investment in building materials offers the greater value.

1750sqft Cape Ranch

If it's not clear why, a quick "how it works" overview might be helpful.  With water-based geothermal exchange systems, water provides or transports energy.  More specifically the system operates in one of two modes; either a supply (in case of heating) or removal of energy (in case of cooling).  The provision or extraction of energy will increase or decrease the temperature of surrounding matter.  The higher or lower the temperature of material, the more, or less, energy it contains. 

Community Geothermal - 10 Buildings on Single Closed Loop

In the case of geothermal energy, we are interested in leveraging or accessing the temperature of the earth’s crust – which has in fact captured and stored the sun’s energy. The rotisserie effect of the earth as it orbits the sun has given the earth’s crust a relatively stable and consistent temperature of 50-55 degF in the Northeast.

When we talk about ground source heat pumps (or geothermal heat pumps) we’re typically referring to a technology that utilizes water to conduct heat or energy from the ground into a heat pump which extracts energy and transfers it to the building through the use and conductive properties of water. 

In conclusion, because the geothermal system depends on water to transport the energy, the more energy required – the greater the water flow needed. The more water, the larger the loop field in the case of a “closed loop” system, or the greater the pump size and well water source needed in the case of an “open loop” system. 

Whether a closed or open loop system, the more water needed the more costly the system and the greater the disparity in initial cost between a traditional heating and cooling system versus a geothermal heating and cooling system.  Therefore it’s not the building size … but rather the building material quality that drive suitability of geothermal technology.