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We want the GarageDominium to be energy efficient, but any upgrades need to have a good payout.  There are a lot of design and equipment options to make very efficient buildings.  However, many of them increase the cost so much that the energy savings doesn’t pay for the upgrade.  Most new homes in this area are using open cell foam insulation.  This is a good upgrade that reduces heat loss/gain as well as reduces air leakage.  Additionally, instead of insulating the ceilings, we will insulate the underside of the roof deck.  This keeps the attic much cooler which improves efficiency.  The exterior walls will be 2 x 6 construction and filled with foam insulation.  The garage and shop will have foam insulation on the roof but fiberglass bat insulation in the walls to reduce cost.  Energy.Gov has a good site explaining unvented (conditioned) attics.

We will also be using a high efficiency multistage heat pump and variable speed air handler.  This will minimize unit cycling and keep thus keeping a more constant temperature and humidity.  We’ve also specified that air leakage must be such that there are less than 2 air changes per hour at 50 pascals (2 ACH 50).  Our house will be in Climate Zone 2; however, Climate Zone 3 is just 10 miles north.  I’ve specified Climate Zone 3 which requires a 3 ACH 50. Zone 2 requires 5 ACH 50. So I’m trying to get a lower air infiltration than required by code. With good construction practices we should be able to get this lower value. 

However, a house this tight can create other problems such as stale air.  We must also balance air flow when bathroom or kitchen exhaust fans are running.  There will be an outdoor air intake that modulates to maintain air balance.  This ensures that most of the air coming into the house is controlled and conditioned.

The Texas hill country seems like a very dry place, but in reality, it gets very humid.  For better humidity and temperature control we will install a whole house dehumidifier upstream of the heat pump evaporator.  It will also supply dehumidified air to the attic.  We considered using an energy recovery ventilator, but local HVAC guys say an ERV can’t handle the humidity load.

Plumbing doesn’t seem all that interesting until it doesn’t work, or it leaks.  One of U.W.’s primary requirements is to have hot water within a few seconds of opening any hot water faucet.  Having lived in houses where it takes many minutes to get hot water out of some faucets, her specification is understandable.  To accomplish this, we start with a large hot water supply.  To save energy we’ve chosen a heat pump style water heater with an 80 gallon tank.  While a tankless water heater can provide hot water almost instantly, we do not have gas and electric versions are not very efficient.  The heat pump water heater has low energy use. It also has the benefit of supplying some cooling to the space where it is installed, in our case the garage.

The next step is to properly size the plumbing.  Water velocity needs to be balanced with water volume in the pipes.  Large pipes minimize friction losses and noise but make for a large reservoir of water that must be flushed before the hot water arrives.  Small pipes can be noisy and can create a lot of pressure drop.  Another consideration is the type of plumbing circuit.  There are manifold type systems, and various branch and circulating systems.  After much study and discussion with the plumbing contractor we decided on a single loop system with a hot water circulation pump. 

The piping will be PEX A which minimizes connections and losses.  The circulation pump uses a smart recirculation controller from Leridian Dynamics.  This system senses flow and water temperature so that the pump only runs when needed.   In addition, all hot water lines will be insulated.  Hopefully this solves the hot water delay problem and keeps U.W. happy.

I’ve described the clean end of the plumbing system, now for the dirty end.  There is no public sewer system in this subdivision.  We will be installing an aerobic septic system.  This is pretty common for the area.  Not much to talk about here other than we are including an extra connection for an RV dump station.