Tag: Energy Recovery Ventilator

Understanding Indoor Air Quality and How It’s Managed in Super-Insulated Homes

As we all work to make our homes more airtight, we also have to be conscious of our families’ need for fresh air — oxygen above all! If our homes were completely airtight, we not only would risk suffocation, we would also be more susceptible to the toxic gases and fumes emitted by our paint, our carpeting, our gas appliances, and more.

The outgassing from our carpet and other building materials are known as “volatile organic compounds” or VOCs.

An appliance which you’ll be hearing more about as homes become better insulated and therefore more airtight is displayed schematically in the third column. It’s called an Energy Recovery Ventilator (ERV) or a Heat Recovery Ventilator (HRV).

Before I explain this appliance’s operation, let me tell you what it replaces: the exhaust fans in your bathrooms and above your kitchen stove. Those exhaust fans simply pump air out of your house, which causes fresh air to be sucked into your house via the gaps around your doors and windows and multiple other gaps you are not aware of.

That air which enters your home is not preconditioned in any way. It is whatever the temperature is outdoors, and in midwinter it could make your furnace work harder heating the cold air which naturally enters your home, whether or not those exhaust fans are operating.

Thus, the primary job of the ERV or HRV is to use the heat from the air being exhausted from your home to preheat the air that is entering your home without having those two sources of air mix with each other.  This is done through a heat exchanger. In the above diagram, the heat exchanger is in the middle of the device. The unit runs at low speed, taking the stale air from your bathrooms and kitchen (typically), through a metallic heat exchanger which then adds that heat to the air which is passing through the adjoining passageway from the outdoors into your living spaces. That fresh air replenishes the oxygen in your home. The picture below is of a typical HRV installation. Both images are sourced from homes.winnipegfreepress.com.

What I have described above is the function of the HRV, which only handles the transfer of heat from one air source to the other. The ERV also performs the transfer of humidity. Thus, if the cold air outside your house is very dry (typical of Denver’s climate), the ERV will transfer some of the moisture from the indoor air to the incoming air.

Neither the ERV nor the HRV measure or react to the presence of toxic gases in your home. That’s the added value of a third device, the CERV or Conditioning Energy Recovery Ventilator. If you’re concerned about indoor air quality, this is the device you’ll want to consider installing in your home.

Whereas the ERV and HRV may operate on an as-needed basis, the CERV is intended to run 24/7, constantly monitoring the level of CO2 and VOCs in your indoor air as it is drawn through the unit. If the levels of these or other pollutants are high, the unit’s fan will run faster. A recent update of the unit has the addition of a virus-killing UV light.

Also, a CERV contains a heat pump, so it can actually perform the function of a furnace, preheating the air which is drawn from outdoors (or recirculated within the house), not merely transferring the room temperature heat from the exhausted air to the incoming air.

I have written in the past about the Geos Community in Arvada. None of the homes in that community use natural gas. Instead, the townhomes are heated and cooled by a combination of a heat pump/mini-split system and a CERV which provides additional heating or cooling. The detached homes at Geos also have CERVs to complement the ground source heat pumps which provide the primary year-round heating and cooling of the homes. 

Learn more about CERVs at www.BuildEquinox.com. The local vendor is Todd Collins of AE Building Systems, 720-287-4290.

A High-Performance Car Can Kill You. A High Performance Home Can Save Your Life.

I have the best assignment on the steering committee of the Metro Denver Green Homes Tour — shooting video tours of the homes we choose to feature. Because of Covid, I’m taking that assignment more seriously than ever, because we may not have an in-person tour this year. (The tour is on October 3rd.)

I post these tours (along with the video tours of our listings) on my YouTube channel. Go there to check out some of the more recent tours.

Those videos, however, are limited in what they can convey in 7 to 10 minutes, so I must leave out a lot of what I learn during the lengthy orientation I get from each homeowner prior to shooting the video.

A good example was my tour last Saturday of Jen Grauer and Josh Renkin’s house in Denver. They scraped a house and built from scratch the best example of a “high performance home” I have come across yet — and I’ve seen a lot of high performance homes.

My 7½-minute tour of the house that Jen completed three years ago could not include a lot of what makes it such a good example of sustainability, so I’ll add to it here.

To be “net zero energy,” a solar-powered home like Jen’s has to be super insulated and super efficient in its use of energy. When a home is that tight, indoor air quality has to be addressed to make the home safe. That job is performed by an Energy Recovery Ventilator (ERV).

The ERV’s job is to bring in fresh air from the outside and to expel bad air while maintaining a healthy indoor humidity level. In the typical home, exhaust fans in bathrooms, kitchens and laundry rooms exhaust air to the outside, thereby drawing fresh air into the house only through whatever leaks exist around doors, windows and other penetrations of the home’s “envelope.” An ERV has one dedicated duct to exhaust air and another to bring in fresh, filtered air. This air is circulated through the house via multiple exhaust and fresh air vents around the home. In addition to maintaining indoor air quality, the ERV transfers some of the temperature (and humidity) of the outgoing air to the incoming air when there is a differential between the two.

Let’s say your home is 70 degrees inside, but it’s 100 degrees outside. The temperature of that incoming air can be reduced to, say, 75 degrees by passing it through a heat exchanger where it doesn’t mix with the outgoing air but acquires some of its temperature. Similarly if the outdoor air is below freezing, the ERV might raise that incoming air to, say, 50 degrees. (I could be way off on these numbers. I’m just trying to convey the concept.)

A conditioning ERV (or CERV) monitors the level of carbon dioxide and volatile organic compounds (VOCs) in the outgoing air. You can set a level that is acceptable (say, 900 ppm maximum) and the CERV will increase the flow of air when those levels are exceeded to bring them back to the acceptable range. Whereas an ERV runs 24/7, the CERV only needs to turn on to bring the levels of CO2, VOCs and humidity down to set acceptable levels. A CERV also has an internal heat pump to add heat or cooling. (See my videos of John Avenson’s and Jim Horan’s homes.)

In Jen’s case, in addition to an ERV, she made sure that the home was built with low-VOC products. For example, instead of using high-VOC particle board, her cabinets are made with zero-formaldehyde birch plywood and her island is solid maple and waterproofed with a zero-VOC oil. Her home has no wall-to-wall carpeting, which typically has VOCs in it. (These items are mentioned in the video of Jen’s house.)

Radon is another pollutant which seeps into every home through their concrete foundation walls and slab-on-dirt. To further improve air quality, Jen installed a radon mitigation system.

In summary, a high performance home can not only save you money in the long run (it costs more to build but nearly eliminates monthly utility bills), it can also create a home than extends your life through improved indoor air quality.

Discover Arvada’s Geos Community, Where the Homes’ Energy Costs Are Essentially Zero

That’s what it’s like for Jim & Patty Horan, who bought their 3-bedroom, 3-bath, 2,135-sq.-ft. home at 15062 W. 69th Place in Arvada’s Geos Community. They paid $525,000 for it three years ago (July 2017). 

Like all Geos homes, this one has no gas service. With only 6kW of solar panels on the roof, the home is heated by a ground source heat pump. It draws heat from the earth via a 300-foot-deep loop under the home. The heat pump uses very little electricity during the summer to further cool the 55° fluid in that loop, and not much more energy during heating season to heat that fluid to 100 degrees.

On Saturday, June 27th, Jim Horan gave me a tour of his home which I recorded for this fall’s Metro Denver Green Homes Tour. You can view the video at YouTube.com/jimsmith145.

Geos Community’s website describes it as “Colorado’s first geosolar development” and is the only subdivision I know that’s built entirely “net zero energy.” There are developers building solar-powered communities like KB Home’s subdivision on the northeast corner of Hwy 93 and 58th Ave., but they don’t come close to being net zero.

There’s a term for such homes — “greenwashing,” which Wikipedia defines at “a form of marketing spin in which green PR and green marketing are deceptively used to persuade the public that an organization’s products, aims and policies are environmentally friendly.” I’ve always marveled that those KB Homes were built with many of the solar panels installed on north-facing roof surfaces.

Getting back to the Horans’ home, there’s more to going net zero than having solar panels and a ground-source heat pump. Those features must be coupled with energy saving features so that the limited number of solar panels are enough to meet the home’s energy needs — with energy left over to charge an electric car.

Here are some of those features which I covered in my video tour with Jim Horan.

First and foremost is the passive solar orientation of the building with lots of south-facing windows and a south-facing roof for solar panels. Also, there are overhangs above each south-facing window designed to shade it from the sun during the summer while allow full sun in the winter when the sun is lower in the southern sky.

Next, the building’s “envelope” has to be very tight. That starts with foam insulation blown onto the interior surfaces of the roof and exterior walls, replacing the blown-in cellulose and fiberglass batting typical of tract homes built by other developers. The windows are Alpen triple-pane windows which also have foam-insulated fiberglass framing. (Fiberglass is better for window framing than vinyl – not as prone to aging and warping.)

Those elements make a house too air-tight for healthy living, so an energy recovery ventilator is installed which constantly brings in fresh air, using a heat exchanger designed so that the heat (or coolness) of the air being exhausted is used to heat or cool the fresh air being brought into the house. A heat pump within this device, called a CERV, provides further heating or cooling of that fresh air as needed.

In the townhomes at the Geos Community, the CERV works with an air-source heat pump mini-split instead of a ground-source heat  pump to heat and cool the home year-round.

Have you heard the term “indoor air quality” or “sick building syndrome”?  It refers to high levels of CO2 or volatile organic compounds (VOCs) which can build up in a home, especially in a home as air-tight as the Geos homes.

The CERV monitors both CO2 and VOC levels in the house and will bring in additional fresh air when those gases exceed the level set by the homeowner. (The Horans have the level for each gas set at 950 parts per million, or ppm.)

What are VOCs?  If you can smell it, it’s probably a volatile organic compound. Examples include new carpet smell and, worst of all, cat litter smells.

Two appliances in Geos homes also contribute to their low energy load. One is the Bosch condensation clothes dryer, which pulls in cool, dry air from the room. The air is heated and passed through the clothes; but instead of being vented outdoors, the air travels through a stainless steel cooling device or heat exchanger. It does heat the room it is in, so the Horans choose to dry their clothes on an outdoor line during the summer, even though their heat pump could handle the additional cooling load if they didn’t do that. Home Depot sells the Bosch 300 “ventless” dryer for $989.

The other appliance is the heat-pump water heater. It has a heat pump above the tank which transfers the heat from the room into the water. I’ve written about this product before. Home Depot sells a 50-gallon Rheem model for $1,299 which earns a $400 rebate from Xcel Energy and another $300 in federal tax credit if purchased by December 31, 2020. Because this appliance emits cold air, it’s in a pantry which the Horans keep closed in the winter and open in the summer. (I would put it in a wine cellar or in a room with a freezer, which emits hot air — a symbiotic arrangement within one room.)

As you are beginning to gather, building a net zero energy home is best done from scratch, when the additional cost is less than retrofitting a home. (My home is net zero in terms of electricity, but we still burn $30 to $50 of natural gas each month, and it takes twice as many solar panels for my home, which has about the same square footage as the Horans’.)

You may be wondering how much more it cost to build the Horans’ house, which they bought new in July 2017. To answer that, I searched all the comparable homes (2– or 3-story, between 1,500 and 2,500 square feet within 1 mile radius) sold during the summer months of 2017, and I found that the $246 per finished square foot paid by the Horans was actually below the median price ($253 per finished square foot) for the seven comparable sales. And those homes probably pay thousands of dollars per year more for electricity (and gas) than the Horans.

If you want to learn more about Geos community, give me a call at 303-525-1851 or visit the Geos website, www.DiscoverGeos.com.

Some Favorite Home Improvements When Purchasing a New-to-Me Home

Who doesn’t want to make some improvements on a home they have just purchased?  Here are some of my personal favorites.

Energy efficiency is very important to Rita and me, so the first thing we do is pay for an energy audit by someone like Andrew Sams of Alpine Building Performance to identify opportunities for making the home more air-tight. This would likely include blowing more insulation into walls or ceilings and caulking around windows. It might also include installing an energy recovery ventilator (ERV) to bring fresh air into the home. This device warms cold outside air in the winter and cools hot outside air in the summer by means of a heat exchanger.

I love bringing sunlight into a home, not with traditional skylights but with sun tunnels. Most people are familiar with the Solatube brand, but I prefer the Velux brand. I had Mark Lundquist of Design Skylights install a 22-inch Velux sun tunnel in my windowless garage and a 14-inch sun tunnel in my windowless laundry room — and four large Velux sun tunnels in the Golden Real Estate office. Ah, sunlight!

Speaking of sunlight, we replaced every light bulb is our house with LEDs which are “daylight” color (like sunlight), not cool white or warm white. CFLs and incandescent bulbs are so 2010!

Installing solar photovoltaic panels is a no-brainer for us, especially now that the cost has dropped so much. Your roof doesn’t have to face due south. Southeast and southwest are good enough. (That’s our situation.) Since you might be driving an electric car someday, install as much PV as Xcel Energy allows to cover that future load.  If you have just purchased an EV, Xcel will allow you to install more panels based on anticipated future use.

Don’t you hate climbing a curb to enter your driveway? Developers install those mountable curbs the entire length of the streets in new subdivisions, not knowing exactly where each driveway will be. One of the first things I would do (and have done) is to hire a concrete company to replace the mountable curb with a smooth entrance. It cost over $2,000 for our 3-car-wide driveway, but I love it every time I enter from the street! Caution: the sidewalk will now be sloped slightly and pedestrians could more easily slip on ice, so be prepared to salt your sidewalk to eliminate icing!

When your gas forced air furnace needs replacing, consider replacing it with a heat-pump furnace or mini-splits. And when your gas water heater needs replacing, I suggest buying a heat-pump water heater. The cost is about the same, and, by converting to electricity for both, you will have eliminated the most common sources of carbon monoxide poisoning in your home.

Other improvements I’d consider include: Replacing carpeting with  tile in bathrooms; and replacing regular glass with Low-E glass on south-facing windows to reduce the harmful effects of sunlight on furniture, hardwood floors and artwork.