[Strawbale] PEX tubing in floors

[David Neeley]

Shody,

There is no "separation" involved. There is heat, or the relative
absence of heat. Heat, being an energy state, tries for
equilibrium--which is why heat always flows to cooler places.

A heat pump moves heat from one place to another. That is why it is so
much more efficient than any fuel-based heat source--it is not
creating it,  merely moving it.

The ground below a few feet is remarkably stable year-round (in any
given place, the stable ground temperature is pretty much equal to the
average air temperature in that location through a year). In most of
the continental U.S., ground temperatures range from the 50s to nearly
70. That means that when a heat pump in cooling mode takes heat from
the air, it can dispose of it in a ground loop since it is far hotter
than the ground is. And, since the ground is an effective infinite
heat sink, its capacity is able to handle that load with little
problem so long as the exchange loop is adequately sized and arranged.

Similarly, since the ground is so stable and within a temperature
range not so far from comfort, when the air is cold outside heat can
be taken from the earth and applied to the air inside. Again, the
ground has ample heat in it for this purpose.

The insulation and sealing of the house mean that it will stay more
uniform in temperature, and that much less cool air is needed to cool
it and far less hot air is needed to warm it. Think of the difference
between keeping a drink in a glass at a reasonable temperature
compared to keeping that same drink comfortable in a Thermos. Less
heat or cold is needed to keep the drink at a good temperature in the
thermos, merely because there is less loss from the drink to begin
with.

The first thing to determine in any given case, though, is what the
house design will do--how much heat or cooling is needed for that
house in that location. That will begin to help you determine the
system requirements.

In any mechanical system, it is always best to optimize it consistent
with the needs of the building. Too much capacity is in several ways
as bad as too little--like Goldilocks, you always seek a solution that
is "just right!"

You should be aware, though, that a superinsulated house is not a
complete "good thing" in and of itself. It is far more subject to
"sick building syndrome" unless great care is taken with its
ventilation, for instance. In fact, many of them need what is called
an "ERV" (energy recovery ventilator). This is a mechanical fan unit
that draws in outside air and exhausts inside air simultaneously. In
cooling mode, the outside air is cooled by exhanging some of its heat
with the outgoing inside air--the opposite being the case with the
heating mode. This means you can have adequate ventilation for health
with very little energy expenditure, while not having to heat and cool
the ventilation air so much.

In any house that is actually well sealed, you must pay attention to
the issue of ventilation. A superinsulated house should always be a
well sealed house--making ERV installation a nearly mandatory feature
in most cases.

Until the recent past, ventilation was almost never an issue since
most houses were poorly sealed. Now that we are paying more attention
to this issue, these are becoming more practical all the time.

David