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Frequently Asked Questions
Why is the ground a better source than the air?
Its temperature barely moves across the year.
It does not track a cold snap or the season.
Output stays steady whatever the weather does.
Efficiency is predictable rather than variable.
There is no outdoor coil to frost, so no defrost cycle.
What are the ways of building the array?
Vertical boreholes, horizontal trenches or open loop.
Boreholes need little land but require rig access.
Trenches need open ground and cost much less.
Open loop draws from groundwater or a water body.
Conditions and consents decide which is possible.
Why is the array sized on the annual balance?
Because the ground remembers what was taken from it.
A loop can meet a design day and still fail over years.
Taking far more heat out than goes back cools the ground.
Performance drifts down slowly as that happens.
Peak load alone is not a sufficient basis.
What goes into the sizing calculation?
Ground conductivity, loop length and spacing.
The seasonal balance of heating against cooling.
The building's annual profile, not just its worst hour.
Site testing informs the conductivity figure.
All of it is settled before drilling begins.
How long does the buried array last?
Normally longer than several machines.
The pipe is inert and undisturbed once installed.
Replacements connect to the same array.
The capital is spent once and inherited afterwards.
That changes how the investment should be judged.
What does an open-loop system give up?
Control over water quality.
Water is drawn from the ground or a water body.
Fouling and corrosion become live concerns.
Abstraction and discharge carry obligations.
In exchange the capital cost is the lowest of the three.
Can the same system provide cooling?
Yes, and doing so helps the ground balance.
The cycle reverses and rejects heat into the array.
That returns some of what winter took out.
Buildings with both loads suit the technology best.
Passive cooling is sometimes possible without the compressor.