The Acadia unit is air coupled, but
according to their literature achieves high efficiency down to very low ambient
temperatures using a "booster" compressor (and perhaps other
proprietary parts or processes). It is my personal opinion that they may
actually have something here, but until a major brand puts their label on the
units, or Hallowell's customer service improves drastically, I'd think twice about
looking at them.

There is no question about it; ground source heat pumps are more expensive than
conventional heating and cooling equipment. The MOST economical thing to
do is to reduce loads as much as possible first. In the case of this
house we have reduced our loads enough to (comfortably) reduce our heating and
A/C equipment by 50%. This not only makes the equipment 50% smaller, but
also reduces the ground connection by 50% (this saves a LOT
of money).

There are a number of ways to couple a heat pump to the ground: horizontal
trenching, vertical boreholes, water loops, standing column wells, and perhaps
others. Each has pros and cons and can drastically affect the cost of the
system. In our case, we are choosing to go with a standing column
well. Why?

A 400' well was installed prior to our purchase of the property. We
have some concerns that the 5 gallons per minute refresh rate is a little low
for our 5 person family and had plans to deepen it regardless (to try to bring
up the refill rate). The general rule of thumb (for the local geology) is
~150 feet of well depth per ton of heat pump capacity. If we deepen the
existing well another 150 feet, we will have more than enough capacity to heat
and cool our house as well as supply us with domestic water.

Well drilling in this area is ~$8-$10 per foot (we hit granite at 30 feet).
Doing some quick math, that will cost us about $1500 (plus some setup
fees). If I had to drill the entire depth, it would cost me $5,500 plus
setup. For the sake of comparison, if we
needed a system that was twice the size (conventional construction), we'd need
an $11,000 well AND spend twice as much on the inside equipment.

I have not had vertical boreholes estimated, but it will require deeper
drilling (the reasons are too technical for this page). Horizontal trenching is difficult in our rocky
soil and can get expensive quickly. In
short, our most economical option of ground coupling is the standing column
well. Standing columns tend to be more efficient
than closed loop systems, but they tend to be less advantageous for homes that
do not us their well for domestic purposes.

The primary cons of standing column wells are: potential mineral fouling of
the heat pump, and the potential for wasting water (if not designed properly).

The moral of the story… GSHP costs add up quickly. My suggestion is to
spend the money on insulation first. Conservation
costs less in both the short and long term.

Ed

Mr. Green Dreams