Designers of energy-efficient homes — especially homes aiming for net-zero energy use — must inevitably grapple with the question of simplicity versus complexity.
Residential designers can choose from an array of sophisticated appliances that improve comfort and help homeowners reduce energy use. Examples include heat-recovery ventilators (HRVs), condensing boilers, ground-source heat pumps, solar hot water systems, on-demand water heaters, heat-pump water heaters, photovoltaic modules, and co-generation systems.
Most of these devices perform well. However, designers who specify sophisticated appliances need to consider the trade-offs that accompany such hardware:
- Higher upfront costs;
- The need for proper commissioning; and
- The need for proper maintenance.
Commissioning? What’s commissioning?
Builders often underestimate the importance of commissioning all HVAC equipment after installation. (“Commissioning” simply means making final adjustments and tuning up equipment to verify that it functions properly.)
Unfortunately, most new homes are imperfectly commissioned, leading to one or more of the following errors:
- The air conditioner has the wrong refrigerant charge.
- The airflow over the cooling coils has not been verified.
- Duct systems haven’t been checked for leaks.
- The airflow through forced-air registers hasn’t been adjusted to meet specifications.
- Pressure imbalances between bedrooms with closed doors and adjacent hallways have not been remedied.
- Exhaust fan airflow hasn’t been tested.
- Heat-recovery ventilators have not been balanced.
- Atmospherically vented appliances haven’t been checked for backdrafting during exhaust fan operation.
- The temperature set-points on the solar hot water system controller are improperly set.
HVAC commissioning errors almost always result in needless increases in energy costs. Many HVAC specialists can share horror stories about commissioning errors, running the gamut from irritating to outrageous (for example, air-source heat pumps with electric resistance elements that operate for most of the winter).
You mean I have to change the filters?
For four years in the 1990s, I provided capital needs assessments — glorified home inspections — for multi-family residential projects in Vermont. During that time, I inspected hundreds of residential buildings maintained by professional management companies.
Almost all of the buildings showed signs of neglected maintenance. Among the problems I saw:
- Crawl space pipes that had been leaking unnoticed for years.
- Fifteen-year-old HRVs with filters that had never been changed.
- Fresh air intake vents for HRVs that were clogged with leaves, cobwebs, and animal hairs.
- An exhaust vent blocked by a bird’s nest.
- Disconnected attic ducts.
- A disconnected furnace flue.
- Emergency lighting with dead batteries.
There’s no reason to believe that American homeowners are any better at maintenance than the average residential property management company; in fact, they may well be worse. That’s why anyone involved with home inspections can share stories similar to mine.
The more complicated equipment, the greater the maintenance headaches
Many of today’s harried homeowners don’t even know where all of their mechanical equipment is located, much less the equipments’ maintenance requirements.
Even well intentioned homeowners sometimes decide that it makes economic sense to neglect equipment maintenance. The classic example: after a few years of operation, many active solar water heaters develop problems — for example, a broken control, a burned-out pump, or a leaking tank. Faced with a repair bill of hundreds of dollars, many homeowners decide to disable rather than repair the solar equipment.
Maintenance costs eat into energy savings
Let’s say you’ve calculated that your new $7,000 solar hot water system will save you $124 a year (the average savings shown in a 2006 study by Steven Winter Associates). Since the equipment helps lower your carbon footprint, you’re willing to accept the fact that your solar water heater has a long payback period. However, the payback period may be even longer than you realize.
After saving $124 per year for five years, you’ve saved $620. But if a failed pump requires a $300 repair, you’ve just seen half your savings evaporate.
Another example: thousands of homeowners have decided to upgrade from a conventional water heater to a Polaris condensing water heater — a sophisticated appliance that is both highly efficient and frighteningly expensive. Unfortunately, many of these homeowners have seen all of their energy savings disappear; the money has been passed to the local plumber who stops by regularly to replace another failed Polaris igniter.
Considering the potential drawbacks of overcomplicated equipment, it’s good for designers and builders to follow these principles:
- Always favor envelope improvements (thicker insulation, better windows) over equipment upgrades.
- When specifying equipment, keep it simple.
- Include realistic maintenance costs in all cost-effectiveness calculations.
- If possible, locate most of a home’s mechanical equipment in one centrally located (and spacious) room.
- Insist that your HVAC contractor show evidence that installed equipment has been properly commissioned.
- Provide homeowners with a three-ring binder that describes the home’s equipment and lists maintenance requirements.
As advocates for the Passivhaus standards remind us, it’s far better to have simple, inefficient heating equipment in a house with thick insulation and triple-glazed windows than it is to have sophisticated HVAC equipment in a house with code-minimum insulation.
For more information on why envelope upgrades make more sense than equipment upgrades, see Equipment Versus Envelope.
Last week’s blog: “The EPA’s Indoor AirPlus Program.”