Deep Dive: HVAC

I evaluated many different forms of heating and air conditioning for my home. Initially I was going with geothermal—it was recommended by my architect, and I liked the idea as it's considered very "green." It remained my plan up until I began researching various geothermal systems; then things went south. Because I don't have a large treeless yard, I'd have to opt for a well-based system, which involves drilling two deep wells—and thus requires two deep pockets to cover the steep installation cost. With a payback period of up to ten years, I just couldn't justify that kind of investment.

It's just as well that I dismissed geothermal as an option, for I also learned that, while it may cool a house adequately, it doesn't dehumidify the air. I've read more than a few horror stories from homeowners who complained of mold, moisture damage, and other issues. Even if geothermal was more affordable, I would never tolerate problems like that.

The next option I considered was radiant heat, using a propane-fired hot water system. But this was quickly dropped owing to multiple problems: in my area, propane would actually be more expensive than electricity per BTU. And many people report that radiant heat has some significant drawbacks. Plus, I'd still need a conventional air conditioning system, which would mean ductwork on top of a ton of plumbing.

I'd also briefly thought about resorting to an "old fashioned" forced hot air furnace, with a pair of "split" heat pump AC-only units. But I kept coming back to the high cost of fuel: oil and propane prices are highly volatile. I'd even considered "alternative" forms of heat, such as pellet stove systems, but these simply weren't practical for a whole slew of reasons, not the least of which was the need to constantly feed them.

Finally, I began researching heat pumps for heating and cooling. A couple of close friends advised against it, claiming in their experience it was inadequate. However, I volunteer at a facility that's heated and cooled with a heat pump, and it's perfectly comfortable all year—not to mention that it dehumidifies perfectly in the summer. The final selling point for me was how economical heat pumps are both to purchase and operate.

My home is quite small, with less than 800 square feet of heated space, so I don't need a monster HVAC system to begin with. Also, I'll have a wood stove in the main living space, where extra heat—if it's ever necessary—would be needed most. As an added bonus, the windowed living space faces southwest, so there should be a small but measurable amount of passive solar heating on sunny winter afternoons. Consequently I have zero concerns about choosing a heat pump system. (Incidentally, it will be a Carrier.)

The interior blower unit will go in an alcove built over the laundry (below), placing it centrally in the house, which should maximize its efficiency. And there's a concrete pad outside, roughly 12 feet away, for the compressor.

I would like to be "greener," yes, but living in the woods precludes any sort of solar-powered system. Besides, the trees help cool my house, so I'm saving some energy right there. The house is 100% electric, so I'm not personally generating any CO2 to stay warm (aside from an occasional fire in the fireplace).

Passive Solar

One of the happy accidents about the house is its orientation: it faces southwest toward a clearing over the Deep Ravine (a.k.a. The View). This direction could not be more perfect, since it provides quite a bit of passive solar energy. The image below offers a sense of the natural light that floods the main living space in the late afternoon, which will be especially welcome—and more intense—in winter months.

Tab A in Slot B

Just as with electrical wiring and plumbing, I enjoy building an HVAC system. But unlike the electrical and plumbing systems for the house, I didn't have plans already laid out before going to work, because I didn't nail down what type of system I'd be using until the house was under construction. Ultimately I made things up as I went along, necessitating a number of minor structural revisions.

Above, I'm posing some fittings temporarily in place to evaluate the viability of various possible configurations. Note that I'm using rigid ductwork. Just as I prefer copper over plastic for water supply plumbing, I prefer galvanized steel over flexible plastic ductwork. Yes, I could complete the whole system in an afternoon using plastic, but there are aspects of it I don't care for, such as its propensity to collect dust and dirt in the ribs, and the need to provide continuous support. System efficiency is also impacted because it requires more force to move air through the ribbed ductwork. But most of all, I feel satisfaction going though the design and assembly processes, particularly problem-solving. As of early November 2017, all of the ductwork is done, and I'm ready to install the blower.

What's a Heat Pump?

A heat pump is basically an air conditioner that can run in reverse. An air conditioner transfers heat from the inside to the outside by means of a compressed refrigerant. A heat pump can also move heat from the outside to the inside by the same means—even when it's very cold outside—by simply reversing the flow of the refrigerant.

There are other types of heat pumps; some transfer the heat using air, others using water. Geothermal systems are actually heat pumps in principle, using water to transfer heat to or from the ground instead of the outside air. Refrigerant-based heat pumps are not as energy-efficient, but their installation cost is significantly lower.

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