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Air-to-water heat pump might be fixed

The air-to-water heat pump saga has played out over six years. It has involved two major equipment replacements, a dozen service calls along with many hours of hassle and uncertainty. The entire story appears in a previous post. That story ends last December with a heating system that was utterly unreliable. I started collecting bids to replace the system with another brand of air-to-water heat pump or a gas-fired tankless water heater.

When I finally decided that there was nothing to lose with the heat pump, I decided to tinker with it. I had noticed that the system always shut down during the heating cycle. (A number of other York air-to-water heat pumps were failing in my area, but they were cutting out during the defrost cycle.) The diagnostic code consistently showed the high temperature discharge error. Each and every time this happened there was frost on the coils. The factory rep and local technicians dismissed the frost, because it was light. They were accustomed to seeing much thicker frost on heat pumps without adverse effects. Nevertheless, this bothered me. I began to correlate the failures with specific weather conditions and confirmed that the failures always occurred when outdoor relative humidity was 85 percent or above. The heat pump operated without apparent problems to temperatures as low as 15°F as long as the humidity was low, but it would ice up and cut out at 34°F if the humidity was higher than 85 percent.

On one of his many service visits, I asked the factory rep to show me how to engage the defrost cycle manually. He pointed out the test contacts on the defrost control circuit board. Using the blade of a flat screwdriver, I could span the two contacts and force the system into defrost mode. Now I had a way to test my hypothesis that the heat pump was not defrosting properly. It was mid-December and weather conditions were ripe for the system to fail. I watched the system closely and engaged the defrost whenever the frost was thick enough to block the space between the evaporator coil’s fins. This turned out to be three to four times a day. With regular defrosts, the heat pump continued to operate for a couple of days. When I stopped the manual defrost regimen, frost accumulated on the coils and the heat pump shut down. Every time the diagnostic code showed high discharge temperature. I was convinced that more timely defrost was the answer. Now what?

I remember the factory rep describing York’s sophisticated defrost programming, so I looked up the service manual for my model on the Web. I found that this line of York Affinity heat pumps shared a common control board. The appropriate defrost program or “defrost initiation curve” is set by positioning a jumper on certain pins on the board. My outdoor unit is four tons and the jumper was set according to these instructions in jumper position four. Since that wasn’t working, I thought I’d just try something different and see what happened. I simply moved the jumper to position three for a three ton heat pump.

The heat pump now defrosts regularly and the coils remain clear. Since making this change in mid-December, the system has cut out only once. That happened a day or two after the adjustment. We have now made it to the end of the heating season and there has never been another equipment shut down, despite many long stretches of time when conditions were ripe for failure. The heat pump has operated through it all. I’m ready to declare short term victory, but have no idea how this will work in the long run or if this solution puts excessive strain on the equipment. Frankly, I don’t care about the equipment, because it was simply unreliable and now it works.

Despite my six-year ordeal with the York equipment, I’m still a supporter of the concept of an air-to-water heat pump combined with a hydronic radiant floor. I’ve talked with others that have installed both Daikin and Unico equipment, and the early reports are positive.

Air-to-water heat pump failure

My family built a new home in 2004, and given my long professional background in energy efficiency, it was only natural to include as many energy features as we could afford. I’ve always recognized that home efficiency starts with a tight, well-insulated building envelope. We selected a general contractor that impressed me with his knowledge of building science and a long history of building homes ahead of the curve. Although not a builder myself, I’ve worked with them for many years. I’ve always believed that a builder develops a “system” that works for him or her, and that as a client I would be wise to adopt that system. In this case the system included  hydronic radiant floors driven by an air-to-water heat pump. When our house was built this contractor had already installed several of these systems with good results. Ours was to be the first of many problematic systems over the next several years.

Repeated failures and costly repairs over the last four years have prompted us to seek estimates for a replacement. We might consider another brand of air-to-water heat pump (aka reverse cycle chiller) or we may simply convert the system to a gas-fired tankless water heater.

(click for a larger view)

The original system (above) was installed in late 2004 by our general contractor. The system is a standard York heat pump mated to a heat exchanger made by Aqua Products.

A Good Beginning

The first heating season was trouble free and the system performed very efficiently. The coefficient of performance was measured 3.5 at 49°F. Even when temperatures dropped to the single digits, the system was able to heat the 1800 sq. ft. home without backup heat. After that first heating season we were pleased and optimistic.

Trouble Brews

In November of 2005, the system died. During this time, the house was heated by a single 4.5 KW electric element in the standard electric water heater that serves as the storage tank. In a perverse way, this was instructive. We were able to measure how much heating energy is required without the extra efficiency of the heat pump.

We called in a well-regarded heating contractor. Several months passed as the system was diagnosed and finally York agreed to provide a replacement compressor, while the local distributor paid the labor costs to install it. The work was finally completed in April 2006, two weeks before we shut the system down for the season. While the system is capable of mechanical cooling, we seldom use it. The new compressor performed well during the following heating season, and again we were optimistic.

(click for a larger view)

(click for a larger view)

Another Compressor Fails

The system stopped working again in November of 2007 due to a failed compressor. This time York agreed to replace the entire outdoor unit with a highly efficient member of the Affinity line. We paid our heating contractor for the labor. The work was completed in February of 2008. For the second time, the system was out of commission during the coldest part of the winter.

(click for a larger view)

Just a week later, this new unit stopped functioning during a moderate cold snap — the temperature dropped to the mid 20s. York’s factory representative was in town to meet with a group of HVAC contractors who had been experiencing problems with air-to-water heat pump systems. He dropped by to take a look and declared that all was well.

In December 2008, about six weeks after the system began operating for the season, the system began to cut out. The diagnostic code indicated high discharge line temperature. The York factory representative again visited the system along with local HVAC technicians. He suggested that the liquid line sensor be moved to a different location. That change has not prevented repeated cut outs, all showing the same high discharge line temperature code. Actually, it seems that the cut outs are more frequent now.

All these problems have occurred within the York heat pump, so we have asked that York cover the materials and labor to fix it. Citing the warranty, which does not cover labor, York has offered only to supply replacement parts.

We have decided not to invest any more of our own money in the York/Aqua Products system, and have started to research a replacement system. We might consider other reverse cycle chillers now available from Daikin and Unico. On the other hand, we may just install a gas-fired tankless water heater.

(Note: This post was originally written in late 2009. Since then there has been a new development and the heat pump may be fixed.)

— Bruce Sullivan

Energy conservation first then solar: the sequence for success

When we built the house in 2004, solar electricity (photovoltaics) was too expensive for us. Since this was new construction, we were able to focus on the most cost effective measures first. I think we succeeded for the most part, although I’ve learned a lot in the last six years and would do things differently. One thing we did get right was the concept of focusing on conservation first. The building site and orientation capture passive solar heat. Because passive solar is mostly a design issue, there is very little direct cost. Just use your noodle and make the right design decisions. The building shell is tight and well-insulated. Spray foam insulation was spendy, but performs very well and never wears out. It was a good investment given the choices at the time, although it’s one of those things I might do differently. Choosing conservation and passive solar was the obvious choice: a no-brainer.

But I wanted to go further, so the next step was some kind of renewable energy system. I had already experienced the joys and savings of solar hot water on a previous house, so I knew I would like it. Plus it’s generally accepted that solar water heating captures more energy for each dollar invested. The actual performance is determined by the local climate (availability of sun) and the equipment selected. In central Oregon, the Sun Earth solar system that we installed is expected to generate 3100 kWh per year of energy in the form of domestic hot water. The performance of solar water heaters varies quite a lot. Performance information is available from the Solar Rating and Certification Corporation (SRCC).

Before incentives, the solar water heater would cost us about $6000. Back in 2004, a photovoltaic system capable of generating the same amount of energy (2.2 kiloWatts) would have cost more than $25,000. So, it made sense to install the solar water heater first and wait for PV prices to come down. Now it was time to think about making the house PV ready. I wanted to do everything possible to prepare the house for a smooth PV installation when the time was right.

The site selection and building orientation that work so well for passive solar also give us a large area of unshaded south facing roof. There’s an old rule of thumb for the optimum angle of a solar collector that says the collector angle should be equal to the latitude. That would be 44°N here. The roof pitch is 6-in-12 or about 21°. Most experts agree that the angle penalty is small, especially because winter sun which benefits from the steeper pitch is not as plentiful anyway. So, my roof is a bit flatter than optimum, but the collectors lay flat and look good.

The solar water heating collectors were positioned off to the side, almost directly above the storage tank in the garage. That left a large open area for PV modules. We relocated a couple of plumbing vents so they would not interfere. Flues, chimneys and surface mounted roof vents would be other things to look for, but we didn’t have any of those. But it’s not just physical obstructions that could foul up a PV installation. Shade is the devil. Even a small amount of shade on a typical PV array can kill production. You certainly don’t want architectural elements, such as dormers or chimneys, sabotaging your PV system down the road.

You also must anticipate the space needed for other system components, including the inverter, meter and disconnect switch. These elements are generally located next to the electric service panel or breaker box. In my case, this all fits within a 3-foot by 3-foot area. One often recommended element is an electrical conduit leading from the electric service panel to the roof. We decided not to spend money on the conduit, because it could easily be run up the side of the house. If a conduit is included in the PV-ready package, you will have to be very explicit about the location of the modules and the wiring.

By 2009, the economics of photovoltaics had changed considerably. State and federal income tax credits along with electric utility incentives were higher than ever. On top of that, the market for PV modules found itself with a supply glut that drove prices to unprecedented lows. This combination of factors brought the ultimate price of a 2 KW PV installation to below $1000. It was time to move from PV ready to PV installed.

$20 a Gallon

I just finished reading $20 a Gallon: How the Inevitable Rise in the Price of Gasoline Will Change Our Lives for the Better by Christopher Steiner. It discusses the changes that will occur in the economy and society as energy (not just petroleum) gets more expensive. The end of SUVs, Mcmansions and air travel seems obvious. Expensive energy also means greater population density, healthier people and more small farms. Some remote towns will die, but others will surge with life. Americans will manufacture products again. We’ll create less garbage, and when we do buy stuff, it will be made of bio-based materials. We’ll wear natural fibers from nearby sources. Exurbs will wither, while dense urban communities will thrive. Many of these developments are poised for rapid growth. The technology is ready. The main obstacle is artificially cheap energy. While none of these are earth-shattering revelations to us greenies, Christopher tells a good story and weaves in many interesting facts to support the theme. If he’s right, we’re on the right track, folks!

Time to support Energy Performance Score

Every car has one. Every appliance has one. Why don’t houses have one? I’m talking about an energy rating. For decades, the biggest energy consuming products have been required to meet energy standards and to display some form of energy use in plain sight.

Consumers need the skinny to make informed choices. Ignorance is the enemy of a free market.

I wrote about one such rating system several weeks ago, called Energy Performance Score (EPS). Energy nerds across the nation are buzzing with the possibilities. Professional conferences, such as RESNET, have dedicated a large portion of their agendas to the topic. The State of Oregon recently passed legislation (SB 79) that established a working group to figure out how to implement the idea. The City of Seattle is running a pilot program that will assign EPSs to about 5,000 homes. Cities and states across the nation are jumping on the bandwagon.

The idea recently made it through the first round of a competition on Change.org and has now moved to the final phase. The winning idea gets an audience with the White House. This kind of exposure is just what the concept needs to make a real difference. If you would like to see energy ratings for houses, please vote for We Must Change Energy Behavior – An MPG Rating for Your Home.

Ductless heat pumps perform well in cold weather

Considering that heat pumps started out as air-conditioners, it’s no surprise that they have a sketchy reputation in colder climates. That reputation is changing now that “inverter driven” technology is appearing in the North American market. An inverter drive system – common in Asia and Europe – is essentially a variable speed compressor powered by a direct current motor. Because they are infinitely variable speed, they operate almost continuously instead of cycling on and off. So far, inverter drive is only commercially available in smaller ductless heat pumps, also called mini-splits.

Compared to their central system cousins, ductless heat pumps are smaller, quieter, more efficient and more comfortable. About the only criticism that remains of ductless heat pumps are lingering doubts that they will work well in cold weather. I’m hoping to dispel that last doubt – at least to a point.

Typical heating systems, whether heat pumps or gas furnaces, operate at full blast for a short time and then shut off. A heating system must be sized for the highest heating or cooling demand of the year even though that “design temperature” is only reached about 5 percent of the time. The result is like taking your car from 0 to 60 mph, then slamming on the brakes, turning off the engine, waiting for a few minutes, and then repeating the cycle.

Not only is that hard on the equipment, but the house never really reaches a stable temperature. Forced air heating systems have large indoor temperature swings. The variable speed nature of the inverter drive system leads to an indoor temperature that stays remarkably constant. This allows interior surfaces to warm up to a stable temperature, too. It is the temperature of these interior surfaces that – more than anything else – determines occupant comfort. This is called “mean radiant temperature.” MRT of 64°F is generally considered comfortable. Gas-fired forced air systems can have variable speed blowers and modulating burners. The problem with furnaces is that you can’t find one small enough for a modern, efficient home.

Of course, applying only the right amount of energy needed to keep the house at the proper temperature is a big reason that ductless heat pumps are more efficient that their central system cousins. But there are several other reasons.

They don’t suffer heat loss in leaky, poorly insulated ducts. Forced air systems lose 20 to 30 percent of the heat between the air handler and the registers. Unless properly installed (and few are), all forced air systems create pressure imbalances within buildings.

Sizing is critical for heat pumps, because turning on and off frequently causes excessive wear on the heart of the heat pump: its compressor. This specialized electric motor drives the vapor-compression cycle that makes heat pumps work. (That’s a whole different topic that I hope to cover soon in an Oikos Library article.)

Because air-source heat pumps extract heat from the outside air, they become less efficient as the outdoor temperature drops. They continue to operate, but the temperature of the air delivered to the building drops, too. Before long, delivery temperature dips to a level that most people will find uncomfortable. To prevent complaints, most heating contractors “lock out” the heat pump when the outdoor temperature reaches 35 or 40° F, even though the heat pump will continue to operate at with an efficiency above 100 percent. Heat is now supplied by the electric resistance elements (strip heat) in the air handler. That’s much less efficient and much more expensive.

Even when outdoor temperature is above 40°F, central heat pumps deliver air to the building at about 105°F and they also move a lot of air within the house. For comparison, a gas furnace will deliver air at about 130°F with lower air volume. This has always been a criticism of heat pumps, because 105°F is not much higher than body temperature at 98°F. This feels cool to most people. Moving a large volume of air at a fairly low temperature is a recipe for comfort problems.

So, the question of whether a heat pump “works” at low outdoor temperatures is really a question of occupant comfort. The answer for heat pumps with traditional compressors, single-speed operation and forced air delivery is clearly NO.

Ductless heat pumps answer every one of these shortcomings.

Sizing is much less problematic with variable speed heat pumps than typical single speed models. Larger units perform better at colder temperatures, but there isn’t the same concern about oversizing. A larger inverter-driven ductless heat pump – meaning more heating capacity – will be able to deliver when the outdoor temperature drops, without suffering short-cycling during warmer weather.

Some continue to doubt that ductless heat pumps will perform at such low temperatures. A couple of years ago, Bonneville Power Administration¹ sponsored research that measured the efficiency of ductless heat pumps in cold climates. Researchers reported that ductless heat pumps delivered 40 percent of their rated capacity at 5°F, with efficiency ratings from 150 to 250 percent. There is also a YouTube video showing a ductless heat pump operating in Manitoba, Canada with outdoor temperatures between 0°F and -14°F.

Across all these criteria, an inverter-driven, ductless heat pump surpasses the typical central heat pump system. Continuous operation allows very low air speed. Lower air velocity improves occupant comfort. Stable room temperatures maintain a higher mean radiant temperature. Larger units can be installed without compromising light load performance. Eliminating duct losses means better efficiency all the time, but especially when outdoor temperatures are low. You can see a list of companies in the Oikos Product Directory under Ductless Mini-split Heat Pumps.

Ductless heat pumps are an excellent choice for new homes that are small and super efficient. You’ll see them in many homes classified as net-zero energy. They can also be good for older homes that want to convert from electric resistance heating, such as electric baseboards or wall heaters . (Of course, a new heating system should always be the last step in an energy makeover that includes air sealing, more insulation and better windows.)

It seems odd to me is that inverter-drive compressors have been slow to arrive in central air-source heat pumps. I predict that manufacturers of central systems are working on that right now.

– Bruce Sullivan

Building hypocrisy in the Malibu hills

Less is more for green building. It must be defined only in terms of using less energy, less water, less material and causing less harm to the ecological processes that support life. I’m appalled that yet another mega-rich celebrity is using “green” to wash away the grime of over consumption.

David Evans, also called The Edge and guitarist for U2 hopes to develop 156 acres overlooking the Pacific coast near Malibu, California. I respect the work that celebrities do for good causes, and I suppose that Mr. Evans has done his share of good deeds. Let’s take nothing away from other accomplishments. Instead, let’s focus on how this particular project reeks of excess.

Mr. Evans’ plans to build five homes on a bluff overlooking the ocean using “every imaginable green building technique”, according a New York Times story. The homes would range in size from 7,000 to 12,000 square feet. Whoa!

I can’t disparage his motives. Let’s assume that Mr Evans’ simply needs some help understanding that “green” isn’t about shiny stuff. Mr. Evans can demonstrate his sincerity by focusing his attention on the outcome not the technology. All five of his houses should meet a few simple goals: net zero energy, net zero water, completely healthy, beneficial to local habitat and certified by an independent third party. I could add more requirements, but I think those five elements should keep him busy enough.

Let’s assume that Mr. Evans is able to meet all four goals and get the house certified. That leaves only a fundamental hypocrisy. He claims he wants to “inspire” others to create a “benchmark of sustainability.” I get it.  A world of eager green acolytes will gaze on this accomplishment and dedicate themselves to building their own multi-million dollar monuments to conspicuous consumption. Let’s see, the land alone cost $9 million, which is more than I would make in… 12 LIFETIMES. And they haven’t even started pushing dirt.

To assert that anyone, but rock stars, investment bankers and mega-millionaires will be able to follow this example is absurd and insulting. It’s bad enough to salve one’s own conscience with green consumption, but it’s contemptuous to say it somehow serves society. I’m sick of rich people claiming that the only reason they build monstrous green houses is to show the rest of us how to do it. If these folks really want to be examples for the huddled masses (who made them rich to begin with), then they should use their money and all their talent to create a truly sustainable home with no more than 500 square feet for each permanent resident. If they need help, I’m happy to offer my thoughts on how to accomplish green development with true elegance.

No matter how many shiny gadgets Mr Evans puts in these small houses, there will be lots of money left over. With that, they could build thousands of truly green houses in Haiti or Africa or New Orleans. David Evans is only the current poster child for this behavior. It happens in every town and to varying degrees. Generally speaking, this kind of greenwashing is unintentional. These folks just don’t get it. Even if Marie Antoinette didn’t really say it, the sentiment applies: “If they don’t have bread, let them eat cake!”

Can passive solar and hydronic radiant heat live together?

We’ve now lived with our radiant floor heat for most of six heating seasons, so I think it’s time to draw some conclusions. The house was built in 2004. Insulation is better than average. The air leakage is impressively low at 1.8 air changes per hour at 50 Pascals. It’s also a true passive solar design with 60 percent of the glazing facing south, high solar heat gain glazing and concrete floors for thermal mass.

Being our first experience with radiant floor heat, we anticipated trotting around barefoot all winter on warm floors. It was immediately apparent that toasty toes were not a given. Because the house is so tight and well insulated, the heating system doesn’t really operate that much of the time. The house requires no heat at all until several days have passed with temperatures in the mid-40s and little sunshine. With the heat system sitting idle, the concrete floor stabilizes at about the same temperature as the room air. That means the floors are considerably cooler than we are. Instead of heat flowing from the floor to us, it’s the other way around. This situation holds true much of the heating season. However, during the coldest, darkest periods, the heat kicks in and our toes rejoice.

Our hydronic system is typical of many radiant floors. Cross-linked polyethylene (PEX) tubes are imbedded in a concrete slab. This slab is only three inches thick and sits atop a typical wood-framed floor. Each of the three zones is controlled by a standard wall mounted thermostat, which measures air temperature. Each zone has a small manifold that feeds three circuits. The flow of water to each circuit can be adjusted up to a maximum of 3/4 gallons per minute (gpm). Over the years, I’ve experimented with different flow rates, and I think I’ve come up with an optimum distribution within each zone.

Zone 1 is the top floor great room with living, dining and kitchen areas. It’s about 600 sq. ft. and contains three large south-facing windows – the source of considerable solar gain. The three-inch-thick concrete floor serves as thermal mass, absorbing heat when the sun shines on it and then slowly releasing the heat throughout the evening. Energy experts often say that this combination of passive solar and radiant floor heat doesn’t work. If the concrete is already warm from the hydronic heat, it will be unable to absorb additional solar heat. That’s certainly correct, but the design of the circuits allows us to have our solar heat and hydronic, too.

The three circuits of Zone 1 are arranged parallel to the south facing windows dividing the room into three sections. The section adjacent to the south windows is turned off entirely because it receives direct solar gain for the entire heating season. We also keep this section largely free of furniture that would shade the floor. The middle section runs at about 50 percent of maximum flow – between 1/3 and ½ gpm. This section receives solar gain only during mid winter when the sun angles are low and light penetrates deeply into the room. The third section never sees direct gain, so the water flow is set to full. This arrangement allows solar heat to be stored while keeping other sections comfortable.

Zone 2 is much different. This zone contains the master bedroom, master bath and the home office. The office has a large south-facing window, but sun can’t strike the floor directly because of desks. The flow rate for this room is about 1/3 gpm or 30 percent of maximum. The bedroom has it’s own circuit also set to about 1/3 gpm. The last circuit in this zone comprises the bathroom and a small walk in closet. The flow is set to the full ¾ gpm. Because the thermostat sits in the bedroom, heat concentrates in the bathroom floors where it stays warm, while the bedroom is nice and cool for sleeping.

Zone 3 is the ground floor containing two bedrooms and a bath for the kids. This zone gets no solar gain, so the flow rate is set to full for all circuits.

With thoughtful design of the hydronic system, I think solar and radiant floors can work together. Credit for this design goes to Jim Chauncey at Sunterra Homes.

That leads us to another question. Is hydronic heat more efficient? Let’s break it down into two parts: distribution and conversion.

Hydronic is a far more efficient way to distribute heat than the most common method, namely forced air. Ductwork is notoriously leaky. Typical duct systems, which are located outside the conditioned envelope, can lose 20 to 30 percent of the heat before reaching the register. Hydronic systems lose virtually nothing. Actual leakage isn’t tolerable as it is with forced air. Plus, the pipes are commonly located inside the building’s conditioned space. What little heat does escape the pipes still flows into the house.

The conversion from fuel to distribution medium is also more efficient. With hard floors, the delivery temperature of the water can be as low as 85°F. It takes less energy to raise the water to this lower operating temperature. Because our hot water is supplied by a heat pump, there is an extra operating advantage to this lower delivery temperature with reduced wear and tear on the mechanical equipment.

Water has a higher specific heat than air so heat transfer within the heating plant (furnace, boiler, etc) is probably a little more efficient than the heat transfer to air. Is this enough to make a difference? I rather doubt it, but I think it deserves mention in the interest of completeness.

The typical advantages of hydronic floor heat obviously still apply. It’s quiet and doesn’t affect furniture placement.

Is high-mass hydronic heat like ours the best choice for a super-efficient house? I will agree with critics to some degree. My current vision of a “perfect” green house is so small and so simple that any type of central heating system is overkill. I would rather spend money on R40 walls, R60 ceilings and the best windows I could afford. The complexity and expense of a hydronic system would be a waste of money and resources.

However, not everyone shares my vision of the perfect house. Many new home designs include a mix of solar-heated space and those with no solar gain. Depending on the design, it may be that hydronic heat is the best approach.

The distribution efficiency might also make it an excellent choice for larger commercial buildings, multifamily buildings and district heating. In these cases, a highly efficient central plant can supply a lot of floor space.

Another advantage to hydronic heat, in general, is adaptability. There are many ways to heat water, including biomass boilers, other biofuels and active solar. With uncertainty about the future, this kind of flexibility may be useful.

So, is hydronic heat appropriate in green buildings? I will avoid making any sweeping proclamations. Instead, I’ll say that “it depends” on the requirements of each project and the care with which the design addresses those requirements.

–Bruce Sullivan

Energy Performance Score: The time has come.

Buying homes is a very emotional process. It’s no wonder that so many people buy energy pigs with lipstick. They look nice, but swill energy. Few people think about how much electricity or natural gas they will have to buy to stay comfortable after purchasing the pig.

Most folks shopping for homes labor under the misconception that new homes use less energy than old homes. There is a certain logic here. New homes tend to have more insulation, better windows and more efficient heating systems. Why, then, do older homes often use less? Take the state of Oregon, for example. I recently learned that the average home in our state uses about 78 million Btus (mmBtu). Based on energy models, we expect a “typical” new home to use about 98 mmBtu. I’m talking about total energy consumption for space heating, water heating, lights, appliances, everything.

After the shock wore off, I started to think of reasons. First, existing homes tend to be much smaller. In Oregon, the housing stock includes homes that are up to 100 years old and most of them are small – between 1,400 and 2,000 square feet. By contrast, the average size of new homes is 2,400 square feet and some are much larger. Size matters.

This brings up and interesting distinction between “efficiency” and “consumption.” Large houses might be called efficient, if they use a less energy per square foot of conditioned floor area than a smaller house. However, the smaller house would consume less energy. Which is more important? Consumption is more important – without a doubt.

Here’s another example. When we built our current house in 2004, we bought a new refrigerator. Comparing the actual energy consumption of several models, I noticed that a 22 cubic foot ENERGY STAR model was expected to use more electricity than an 18 cubic foot refrigerator without the ENERGY STAR label. The larger, more efficient, model would use more energy than the smaller, less efficient, one

There’s been some debate among energy nerds about a term known as Energy Utilization Index (EUI). This term expresses building efficiency as energy per square foot of conditioned space. Some nerds also argue that climate must be factored in, so that those unfortunate enough to live in cold areas are not burdened with guilt for using more energy. Climate matters, too.

As we move into the age of carbon footprints, we need to focus on consumption. It’s the bottom line. Consumption is what you pay for. Consumption generates greenhouse gases and toxic pollution. Consumption must be the yardstick that we use to set energy targets and measure our progress toward those targets.

Which brings us back to helping homebuyers choose houses. Technically speaking, it’s not high efficiency we want to sell, it’s low energy consumption. There are a number of proposals floating around for labeling systems that rate a home’s energy performance and then slap that rating on a label in order to communicate the information to home shoppers.

The system I prefer is called Energy Performance Score, because it shows consumption directly. Using the example of Oregon homes, the average home that consumed 78 mmbtu would have an EPS of 78, while the new home that consumed 98 mmbtu would have an EPS of 98. Simple, huh? The EPS value is the building’s total energy consumption in Btus without all those pesky zeros. Like a golf score, lower is better. When you get to zero, you have a zero energy building.

EPS wasn’t the first energy rating for homes. The Home Energy Rating System (HERS) created and administered by RESNET goes back to the late 1970s. The HERS rating is the standard energy rating approach for residential buildings. It is recognized by government agencies and lenders as the basis for energy efficient mortgages.

While HERS has been available for decades, it has two flaws. It ignores both climate and building size. A 4000 square foot house in Maine could have the same rating as a 2000 square foot house in Arkansas even though the actual energy consumption was starkly different.

In addition to the energy consumption score, the EPS process generates a carbon score based on the amount of electricity and natural gas used and the carbon released in order to bring that energy to the home.

I should emphasize that EPS and HERS are projections using computer models, not measurements of actual consumption. The number of people in a house and their behavior will have a big impact on the monthly consumption. This is impossible to model accurately with a computer. What they do model is the structure and equipment of the building that enable occupants to achieve low energy use. Without good energy bones, occupants are unlikely to achieve the desired results.

So, my preference is the EPS system. (And, it has nothing to do with my day job at Earth Advantage.) A metric based on consumption is simple and direct. It gives builders, real estate brokers, lenders a clear way to communicate the actual energy consumption of homes. It gives homeowners an idea of where they stand and motivates them to improve. It allows society to set measurable goals for performance. It drives the housing market to build better houses.

If you agree that we need a clear metric to express the energy consumption of homes, you can give the idea a big boost by voting on Change.org. Ideas with the most votes may get the ear of the White House. The page titled We Must Change Energy Behavior – An MPG Rating for Your Home explains the EPS procedure and gives more great reasons why we should move forward with this idea – whether or not it gets an audience with the Obama Administration.

The EPS value should be published in real estate advertisements, included in multiple listing services and printed on standard appraisal forms. Every home placed on the market should have an EPS number just as every car on the lot carries an EPA mileage sticker.

Lessons Learned from a Green Building Project

Last month, we rounded out the fifth year living in our green home. It seems like a good time to look back at how it all worked out. I plan to write blogs on several topics, including actual energy performance vs expected performance, the value of simplicity, financial analysis, and the life span of air sealing.

You can see a detailed description of the house and all the green features in the Oikos Project Showcase. Here is the first installment. This one came to me even before construction was complete.

Lesson 1: Trust no one, check everything

Take nothing for granted. Despite the best of intentions and very clear drawings, a couple of features failed to make the trip from plans into the real world. One example is the ventilation system. The ductwork for our energy recovery ventilator (ERV) is completely snarled (see photo). On paper, everything looked great. The duct runs were short, straight and smooth. Reality turned out differently.

ERVs (and their cousins heat recovery ventilators) are uniformly designed so the duct connections leading to the outside of the building are on one side of the unit and duct connections leading to the inside are on the other side of the unit. This facilitates an orderly and efficient duct layout. Unfortunately, the installer cut holes to the outside so that the supply ran to one side and the stale air outlet to the other. No matter which way the ERV box was oriented, one of these ducts had to make an immediate 180 degree turn. That adds resistance equivalent to about 40 feet of straight duct. It’s true these two portals must be far enough apart that stale air can’t be sucked back into the fresh air inlet, but six feet of separation is generally considered enough.

The biggest problem occurred with the duct that delivers fresh air from the ERV to the house. The designer and I carefully considered how this duct should run. A series of chases were designed and built to carry ducts through the building. The stale air exhaust duct and this fresh air duct would occupy the same chase to the ground floor bath. Then a smaller chase would cross a narrow hall to carry the fresh air duct to the ground floor bedrooms. It was clean and simple.

Instead of following the plan, a second fresh air supply run was added from the mechanical closet where the ERV sits to the ground floor bedrooms. That in itself wouldn’t be bad, except the two fresh air delivery ducts originate on opposite sides of the ERV, forcing the use of a T-fitting just a foot from the ERV housing. Air leaving the ERV immediately slams into this T.

Despite careful thought and planning, the guy on the site did it wrong. I’m sure there was a reason, but I’ll never know what it was. Is this a fatal flaw? No. The ERV delivers 80 percent of it’s rated capacity at full power. But some air flow is lost, and the electrically commutated blower motors (ECMs) certainly have to use more electricity.

The real point is that even people with the best intentions can’t get everything right all the time. The construction process is so fragmented that quality control procedures are essential. Quality control is the responsibility of the general contractor. In this case, I will share the responsibility, because I should have caught the problem earlier.

There is another short story that illustrates the need to check everything. Construction was started in April of 2004. You may recall that the ban on pressure-treated lumber using chromated copper arsenate (CCA) took effect that year. The ban meant that no products could be manufactured with CCA after January. However, product already sitting in warehouses could be sold. Well, we specified in the lumber order that no CCA lumber should be used. I happened to visit the site just after the ground floor framing had been completed.

Pressure-treated lumber was required for the mud sills and the bottom plates of all the walls, because they sit on concrete. I saw a partially used stack of treated lumber and casually looked at a small tag that was stapled to the end of the each stick (see photo). The lumber yard had delivered CCA. I called the salesman. He said, “The sticker is wrong.” This response has become an alarmingly common reply. Since that day, I have heard many sales reps utter these words in defiance of clear evidence and common sense. If the label actually applied to a product is “wrong” how could we possibly know what is right?

The unused CCA lumber was replaced with something less harmful.I think the salesman was afraid that I would demand that the installed material be ripped out and replaced too. I didn’t think that was necessary.

There are hundreds of products and materials delivered to every job site. How many of these are wrong? Too often, installers substitute materials or make installation errors that are never caught. Green building is far more susceptible to this problem than typical construction, because green projects have more components that are out of the ordinary.

I’m confronted with this issue frequently in my capacity as a green rater for Earth Advantage Institute. While certification will not solve all the problems, it can reduce blatant errors and help to ensure that home builders and home buyers get what they pay for.

Bruce Sullivan

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