The Energy Audit

Sooner or later it’s worthwhile to call in an expert:

A two-story house can get by with two ductless mini-splits, to provide precise temperature control in all the main rooms of a home.

An old, single-pane window with a low-e storm window performs as well as a brand-new, low-e double-pane window.

A hand-held thermal imager (“infrared scanner”) detects thermal leaks around power outlets, along the baseboard and ceiling molding, and around windows and doors. You can use it inside our outside and before and after adding insulation or plugging air leaks. (Keeps contractors honest.)

Every energy auditor is supposed to interview family members about health concerns that may be caused by bad air quality (e.g., products of combustion from gas appliances, CO2 buildup from too-tight a building shell).

Replacing all the windows in your house with “energy efficient” windows (especially if you already have double-glazing) won’t save more than 1 to 4 percent on your utility bills. Given the expense of that undertaking, it’s not often worthwhile.

You only need one outside door in the winter. Seal tight all the other entries and pad them with “removable insulation.”

A make-do seal in frigid weather: tear cloth strips, soak them in water and wring them dry, then stuff in the door cracks. They’ll freeze and expand, sealing. (Water expands when it freezes.)

A blower door test of the air-tightness of a house indicates if (1) whole-house ventilation with a fan is needed, (2) your home meets minimum ventilation standards, or (3) you’re in serious need of air-sealing efforts.

Energy specialists pressure-test your house with an air blower to identify the worst leaks. Then they use advanced diagnostic methods (and years of experience evaluating houses) to find all the hidden, hard-to-find problem areas.

If your water heater is electric and natural gas service is available, think hard about getting a natural gas water heater. A heat-pump water heater is very efficient, too.

Radiative walls (with hydronic piping inside) can heat (or cool) a space, either independent of the existing forced-air system or as an add-on system. The hot water for space heating can come from a passive solar energy-storage wall, a rooftop solar water heater, or even a gas-fired furnace.

Eliminate overcooling your house by increasing the thermostat setpoint in the summer (lowering it in the winter vs. overheating).

Heat Recovery Ventilators recover up to 80 percent of the heat or cold from exhausting air to temper incoming makeup air.

Radiant floor heating systems versus forced-air heating have lower (zero) noise, better temperature distribution, increased thermal comfort, and up to 30 percent energy savings.

A zone-based thermostat controls the HVAC service to a particular room or rooms, via damper(s) in the ductwork and a local, zone thermostat.

Daylight harvesting uses sensors to monitor light levels near windows or other daylight sources, turning off artificial illumination when the daylight is adequate. A solar room can provide half of your home’s heating needs in the winter.

Seventy percent of the heat in sunlight is in the infrared spectrum and isn’t visible to the human eye. Apply an infrared-blocking film to a window to block out that heat but not affect the view.

If you want quality, guaranteed energy-efficient appliances, look for the Energy

Star approval. Better yet, get one of the “Energy Star Top Ten” appliances. Energy Star has strict standards that ensure the best possible energy efficiency at the most economical price.

Yellow flames on a gas-burning appliance mean the gas isn’t burning efficiently (it should be blue), and it’s time to call a technician for a tune-up.

High water pressure causes faucets to leak, commodes to run, and you use too much water for bathing and household tasks. (High pressure = high volume.) A plumber or the water company can install a pressure-reducer at your water meter to get the water pressure down to normal.

Setting the thermostat back 10° F for eight hours each night saves 7 percent on your heating costs (10° F higher in the summer).

Ductless mini-systems are a good option for room additions, for houses with no ductwork (e.g., with existing hydronic heating), and for rooms that aren’t attached to the main house.

Go to EnergyStar.com and their Rebate Finder to see what kind of rebates for energy-efficient projects are available in your area.

Henceforth, we have found many new ideas, things you won’t find in many books on the subject. Why? Because this book includes some fundamental theory.

When you investigate the science, you find a wealth of new applications. This section goes even further and provides a powerful engineering spreadsheet that does all the standard calculations.

 19.1 THE PRODIGAL HOME PERFORMANCE CONTRACTOR.

The “energy audit” experts suggest ways to save energy (that usually cost a lot of money). If you do your homework beforehand and your building envelope is secure, the windows clean, and so forth, the “energy audit” can save you even more.

Make it hard for the energy professional to find new ways to save energy! Get your money’s worth out of their investigation. Brag about all the things in this book that you’ve done, so they’re less inclined to try and hoodwink you into expensive projects with a low payback.

 19.2 ENGINEERING ANALYSIS 4 DUMMIES.

Thus far, savings estimates have been done by fuzzy, hand-waving math. We need a better way. We need to quantify our decisions.

“Payback” is equal to the total installation cost divided by the annual dollar savings in utility costs. The install price is straightforward. Any certified contractor can give you a quote.

The estimated annual savings is a little more challenging. If it’s an expensive project, you can reasonably ask the contractor to estimate the savings. Most manufacturers have computer programs to calculate savings for their products.

There are two types of engineering analyses: peak HVAC loads and annual HVAC loads. The peak load is used to match the capacity of the heat pump to the size of the building load. The annual loads calculates the total heating and cooling costs over a whole year.

You only need a peak load evaluation if you’re purchasing a new central HVAC system (not an option here until you’ve done all the other projects in this book because their goal is to reduce your peak load).

Annual loads quantifies the energy savings from major retrofits to the building envelope, among others.

 19.3 THE ENERGY AUDIT—BETTER THAN AN IRS AUDIT!

There are several ways to calculate annual heating and cooling loads and many computer programs to perform the analysis. Some contractors are certified to do nothing but energy audits. A full energy audit looks at the whole structure, or all the engineered systems. If all you’re looking at is a roofing project, however, the roofing contractor has accurate tools to analyze just that element of the building envelope. However:

Can you trust the results? “Of course, that fancy, new roof is going to save you a boatload of money – here are all the numbers!”

I hope you’ve learned enough so far to ask the contractor: (1) exactly how many dollars will this project save me on my utility bill each month, and (2) how long is the warranty on the installation?

Almost any new upgrade to old technology saves you money. The critical information is how much and how long is the payback? In other words: “How long before I start saving money?”

Everybody is a used car salesman. They take advantage of your desire to save energy and emphasize that aspect of their product. They hedge when you ask, “How much energy” and get even more squeamish when you demand, “How much money will it save?”

They might even have an elaborate “case study” of the perfect house in the perfect weather with no margin for error: pages and pages of numbers and graphs that “prove” their product will do everything they claim.

Wouldn’t you like to say, “here’s my computer program. Plug in your numbers and prove it?”

 19.4 WALL ASSEMBLIES ARE COMPLICATED.

One note of caution when doing energy calculations: The U-value of any wall assembly is always less than the U-value of the insulation in the wall. Why? Because 80 percent of the wall is efficient fiberglass insulation and 20 percent of the wall is wood, a thermal bridge. Then you add siding, gypsum board, and so forth, for a wall assembly. One of the spreadsheet “tabs” gives typical U-values for different types of complete wall assemblies. (Most of the data is out of date. Find new results online!)

Imagine a commercial building with steel studs, a common construction technique. Steel isn’t an insulator; it’s a thermal conductor! Steel is fast, durable, reliable, and inexpensive, but it conducts electricity. Wood studs aren’t quite as bad, but they aren’t a fraction as good an insulator as fiberglass batts.

In other words, even the simple U-value of a wall isn’t a given but a calculation!

 19.5 CHOOSE YOUR PROJECTS CAREFULLY.

This book focuses on projects that don’t cost very much, if anything. I explain how and why they save energy. However, let your contractor, the manufacturer, or a certified energy analysis do the all-important payback calculations. The more complicated and expensive the project, the more highly qualified and experienced the expertise required, up to a licensed Professional Engineer.

The only major projects recommended here are those which you need to do anyway. If your roof is worn out, pick the right color for your climate. If your refrigerator is on its last legs, replace it with the most efficient model you can afford. If you purchase a new stove vent hood, be sure the exhaust from the vent fan goes to the roof or out the rear wall (i.e., outside the building envelope).

Other than that, I recommend extreme caution for major, high-dollar projects. Unless you have single-pane windows, new windows rarely pay back. No project pays back in a second home that’s rarely occupied. Get plenty of good use out of your existing heat pump before you consider upgrading to a new, more efficient model—and not before you do everything you can to reduce the “peak load.” (Because, having done the projects, the new unit will be much smaller than your existing one.)

Finally, if you’re spending big bucks on a whole new HVAC system, you have every right to ask the contractor to do a comprehensive, official “peak load” calculation to match the capacity of the new system to your heating and cooling loads.

Contractors don’t like to do calculations, but they’re not hard to do, and you can reasonably expect them to crunch the numbers. Don’t let them ballpark an estimate or tech-talk you into their selection.

“I want to see your peak load calculations!”

 19.6 IF IT USES ENERGY, YOU CAN CALCULATE HOW MUCH ENERGY.

Contractors can do all the official calculations for houses. (“Residential Manual J

HVAC Loads.”) Every new home should have this analysis done, and any new HVAC system in an old house, if you’ve changed anything (roof color, attic insulation, remodeled rooms, etc.)

Ask for “a peak load analysis”; demand it!

Why does your contractor need to calculate the air to supply to each room? Because those values determine the size of the duct going to each air supply grill. Air exits the unit at a constant pressure. This air is divided into any number of branches of varying lengths. Each duct branch must carry a fixed volume of air to satisfy the heating and cooling loads of the “zone” (room) served.

How can we be sure each zone gets the air volume it needs? Do you put a small damper in each duct? No! We size each duct run so that the static pressure is equal for each branch off the main line. We use a “Ductolator” (with sliding scales like on a slide ruler, except these tools are circular) to figure out the static pressure for each duct run. Each turn, elbow, or fitting adds a bit of static pressure, as does the discharge grill at the end.

It’s not a simple thing to send more air to one room or another in your house. “It’s always cold/hot in that room.” It could be you just smashed a duct in the attic, cutting off the airflow. It could be much more complicated—it probably is!

The go-to first response to air-supply issues is a pressure test of your ductwork. The technician seals off all the vents, then hooks up a giant fan to the system to see where the leaks are. Once they plug the leaks and get the system back to the original design condition, you can start troubleshooting issues.

Can you see how a new HVAC unit needs the same size fan to move the same volume of air as before so that every room in the house gets the correct volume of air it needs? Even if it’s a smaller-capacity condenser (thanks to all the energy-saving projects you’ve done), the new fan must be sized for the same static pressure because you’re using all the old ductwork again.

If you do a major renovation and need a new air-duct supply? Be sure to put the ductwork in the attic or under the floor in a crawl space, so it’s accessible. (Better if it’s outside the building envelope.)

 19.7 SHOP AROUND FOR UTILITY REBATES.

If you’ve reached the point of getting an energy audit from a certified contractor, it’s a safe bet you’re thinking of making a significant investment. If so, see what rebates are available from your utility company. Commonly, they give high-dollar rebates for high-efficiency HVAC systems (your contractor may even deduct the price directly off the installation cost).

Utilities also have rebates for energy-efficient windows (usually a very long payback), adding attic insulation, a programmable thermostat, air-sealing the house or the ductwork, and even a hybrid (heat pump) water heater. The utility company might even defray part of the cost of an “energy assessment,” alias the energy audit, by a licensed professional.

State and local taxes often have deductions for energy-efficiency improvements, including for solar- and wind-power projects. Every rebate or tax deduction helps not only with the up-front costs but also with the payback calculations. Also, some lenders offer low-interest loans for projects that save energy in your house.

Your energy assessment specialist is probably knowledgeable about all options available in your area and can direct you to lenders who will have your back. Also, check the “Rebate Finder” on EnergyStar.gov.

 19.8 DUCT SEALING FOR FORCED–AIR SYSTEMS.

It’s not uncommon for a duct system to leak 15 to 20 percent of the air volume. All that energy is lost if the duct is in an unconditioned space (attic or crawl space). Moreover, those leaking ducts transport extra humidity into the conditioned space, adding to the summertime HVAC latent load.

An AC contractor can test your ductwork for air-tightness. They seal off the supply registers and pressurize the system with an air blower to see how much air escapes, where, and at what pressure. The contractor can then seal off all the leaks for about $200 and lower your bills by up to 25 percent.

If your annual cost for space heating is $400 (assuming you have a heat pump), then a duct repair job for $200, saving you 25 percent or $100 a year, pays off the investment in two years. That’s an excellent return on your money.

19.9 WHOLE–HOUSE FANS FOR HOT AND DRY CLIMATE?

A large fan mounted in the ceiling at the highest point in the house can draw cool outside air (aided by the “chimney effect”) through the home for free cooling— typically at night, humidity permitting.

In arid climates, the temperature drops 20° to 35° F each night, and the dew point is still in an acceptable range.

A thermostat (perhaps with a humidistat, to measure humidity) controlled whole-house ventilation system turns on after sunset when the outside temperature drops to 70° F and runs all night. After sunrise, when the mercury reaches 75° F, the fan turns off. The homeowner must then close all the windows and, as needed, turn on the air conditioning.

19.10 INTEGRATED WHOLE–HOUSE SYSTEMS GET THE JOB DONE.

In hot and dry climates, energy-intensive refrigeration isn’t the only option for cooling. A single system can control several levels of tech in your house:

1. Whole-house fan
2. Air conditioner
3. Indirect water heater

In the summer, the system monitors outside air temperature and dew point, to use outside air when possible for cooling. It uses the AC only when it’s either too hot or too humid outside. A whole-house fan uses far less energy than air conditioning (although it does need open windows in each room for complete air circulation, or at least an opening in an outside wall with a backdraft damper).

In the winter, there may still be afternoons when the whole-house fan can circulate air. A heat pump or a water-to-air heat exchanger extracting heat from a natural gas water heater can provide space heating.

19.11 HIGH TECH SWAMP COOLER FOR THE NEW–AGE REDNECK.

Dry-climate locations can also take advantage of new, indirect evaporative cooling systems. These systems have a counter-flow heat exchanger that doesn’t add extra moisture to the air like swamp coolers. Indirect evaporative coolers supply six tons of cooling for 1,200 watts, versus 8,000 watts for refrigerant cooling. That translates into an efficiency rating or EER of forty—four times better than the most energy-efficient heat pump system!

The indirect system uses the evaporative cooling of water as the refrigeration method, so you need a ready source of water. When you calculate payback, be sure to add the cost of water to the operating expenses.

 19.12 COLD THERMAL ENERGY STORAGE SYSTEMS ARE BACK.

Commercial ice harvesting systems have been on the market since the nineties. The idea is to use a refrigerant AC system to create ice during off-peak hours (e.g., at night when the electric rates are much lower), then get the cooling you need during the day by melting the ice. The latter involves only a fan, which uses much less energy than an AC compressor.

Until now, thermal storage was presented here only as a passive, often solar, means of storing heat. This method stores thermal cold as ice, a new take on the thermal mass idea.

Packaged “ice harvesting” systems are now available for residential applications. Homeowners can take advantage, just like commercial utility customers, of new off-peak rate structures (if your utility offers demand rates for residential users).

If the “cold storage” method uses 10 percent more total electricity than straight on-demand air conditioning, making ice at kWh rates 50 percent lower, this nets you a 40 percent savings on your utility bills.

 Future Tech!  

19.13

Any major HVAC renovation, to qualify for a rebate from the utility, should require a peak load calculation to be submitted by the contractor (and kept on file for future reference).

19.14

Window retrofits should require a peak load and annual HVAC load analysis to provide an accurate payback value to the customer (and rebate agency).

19.15

All new home construction should be required to pass a “blower test,” and if it’s a “tight construction,” there should be an outside air intake and blower at the HVAC unit, rigged to a CO2 sensor and alarm.

19.16

Federal tax credits for energy-conservation projects should require a minimum payback: The longer the expected lifetime of the equipment, the longer the allowable payback.

19.17

Mortgage companies, in addition to a mechanical and termite inspection, should lessen their risk by also requiring a formal energy audit of all new properties.