Simplicity versus Complexity
Complicated equipment has a downside
Designers of energy-efficient homes — especially homes aiming for net-zero energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. 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(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. 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 commissioningProcess of testing a home after a construction or renovation project to ensure that all of the home's systems are operating correctly and at maximum efficiency. ; and
- The need for proper maintenance.
Commissioning? What’s commissioning?
Builders often underestimate the importance of commissioning all HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. 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 backdraftingIndoor air quality problem in which potentially dangerous combustion gases escape into the house instead of going up the chimney. 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 footprintAmount of carbon dioxide and other greenhouse gases that a person, community, industry, or other entity contributes to the atmosphere through energy use, transportation, and other means. , 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 binderGlue used in manufactured wood products, such as medium-density fiberboard (MDF), particleboard, and engineered lumber. Some binders are made with formaldehyde. See urea-formaldehyde binder and methyl diisocyanate (MDI) binder. that describes the home’s equipment and lists maintenance requirements.
As advocates for the PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. 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.”
- Andy Shapiro
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