Get Big Pivots

The older house had solar panels front and back — and new windows, too. The first clue of deep problems was an air conditioner that couldn’t keep up with the heat, even during May.

 

by Steve Andrews

Energy Waves

Our son bought a small house in Denver in early 2020. It fit his budget and, at least on the outside, looked to be an investment in our energy future. It had solar panels on the roof, front and back.

Sadly, we learned that the house was a poster child for how not to “go solar.” It was back-asswards solar.

The problem became apparent during a May heat wave soon after he moved in. The house, our son reported, was very uncomfortable. Once the outdoor temperature hit 95 degrees F, the relatively large and new-ish air conditioner couldn’t keep the house at 78 degrees even when running 100% of the time.

Thanks to most of the windows facing east and west, the house was a summertime solar collector that would warm into the low 80’s during late afternoons.

The regular home inspection had not revealed that the home was a thermal disaster.

It had no wall or foundation insulation, just three inches of attic insulation, and leaked like a sieve. Also, the ductwork didn’t allow enough airflow for cooling. A thermal inspection using an infrared camera in combination with a blower door and duct blaster to test the house and ductwork tightness was necessary to diagnose the problem.

Installing solar panels above an energy sieve doesn’t make financial sense. With an older home, such as this one, built in 1942, the first step should always be to upgrade existing energy features before even considering adding PV panels. Putting lipstick on an energy pig still leaves you with an energy pig.

Six energy upgrades cut this home’s energy consumption for cooling and heating by two-thirds while delivering a much higher comfort level.

The first and easiest happened before the testing was completed. The duct-blaster test showed that the home’s return-air system was undersized for what was needed to carry the air conditioner’s flows. To correct that, one return-air duct in the floor was doubled in size. The task took just 10 minutes with a reciprocating saw. This allowed the AC to maintain a 78-degree indoor temperature without quite running 100% of the time on the hottest summer day.

The lesson here? Performance testing can guide upgrades.

Next my son and I replaced the attic access door. It was a warped bifold panel in a vertical knee-wall into the attic that never stayed shut (no stops for weather-stripping). The blower-door proved this to be the home’s largest single air leak. We replaced it with a tightly sealed, “stopped” and double-latched plywood door.

The next four improvements were all completed by an insulation contractor several months later.

He sealed numerous air leaks, starting with foaming the always-leak-prone attic floor. Overall, tightening the home reduced leakage by nearly 75%.

Next he blew R-40 insulation above the existing R-10 attic insulation. The code in Denver is R-38. He also drilled-and-filled closed cathedral-ceiling cavities in the areas above and near the attic hatch.

After that he drilled holes in every exterior wall cavity, through the interior drywall or plaster, and blew in loose-fill insulation. That improved R-0 wall cavity insulation to R-15, which is still a bit less than the minimum R-19 wall insulation requirement for a new home in Denver.

Finally, the contractor installed a whole-house fan with motorized insulated cover (R-20). Once outdoor temperatures in the evening drop below the indoor temperature, our son opens a few windows and turns on the 1,600 cubic-feet-per-minute fan. The fan uses a small fraction of the air conditioner for cooling. He turns the fan off and closes windows after breakfast, by which time the house is cool enough to coast well into the afternoon. Air conditioning is needed on only the hottest summer days.

Whole-house fans provide limited help in cooling during the July-August monsoon season. During the monsoon, nighttime outdoor air temperatures can be too warm [mid- to upper-60s] and too humid for multi-day stretches of time, to provide effective cooling when circulated within the home.

Misplaced priorities were also evident in the windows. The previous owners had replaced the original single-glazed windows with efficient low-e windows. The big irony here?

Replacing windows is the lowest priority on the energy-saving scale; you can usually only justify window upgrades on the basis of enhanced resale value and improved indoor comfort.

What about HVAC (heating, ventilation and air conditioning) equipment? The furnace was reasonably efficient and almost new. It didn’t justify replacement.

The air conditioner was plenty big. It’s worth noting that some HVAC contractors, when faced with a comfort problem, blame insufficient equipment size. That answer wouldn’t have worked here. A larger AC unit would have instead exacerbated the insufficient airflow and comfort problems.

Nearly $7,000 was invested in these upgrades. What savings have they produced? Inadequate records by the previous owner and poor feedback by Xcel Energy, the electrical provider, to solar customers precludes a complete answer. Somewhat anecdotal evidence suggests a two-thirds reduction in annually heating and cooling bills. It is also a more comfortable place to live – and, at resale time, the home should be worth more because the improved energy features can be highlighted, not hidden, from the next buyer.

In the future trend toward “electrifying everything,” would it make sense to convert this home to all-electric? Maybe in 15 years, when it comes time to replace the current AC and furnace units. By that time, the cost to install a high-efficiency air-source heat pump will come down enough to warrant the switch.

An air-source heat pump can both heat and cool a home. It uses long-established refrigeration technology to move heat from indoors to outdoors during the summer and scrubs low-grade heat energy from the outdoors and transfers it indoors during the winter. They were originally developed for climates with higher cooling than heating requirements, but thanks to refinements, they are increasingly efficient in climates with more heating than cooling needs. An upcoming article will do a deeper dive into this technology.

So how smart was the previous homeowner when they chose to install solar panels on this energy sieve? Crazy dumb.

The bottom line here? Don’t even think about either “electrifying” or putting solar on an older home until all cost-effective energy-efficiency upgrades have been studied and installed.

Steve Andrews is a retired energy consultant. His experience included consulting work with utilities, builders, state energy offices, and PBS-TV series, plus free-lance writing in the energy sector.

Steve Andrews
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