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Fresh Air and ERVs

by David B. South

The Issue

How do you bring fresh, breathable air inside the home without losing the dome's energy efficiency?

Carbon dioxide gas (CO2) has many sources. We produce CO2 when we breathe and plants give off CO2 when the sun is not shining. (They give off oxygen when the sun is shining.) Combustion also produces CO2, as do coal-fired energy plants, cars, trucks, etc.

High levels of CO2 in a home can be indicative of poor overall air quality. For instance, one can assume that if CO2 levels are high, so are other pollutant levels such as outgassing from carpets or furniture and pet dander.

Since June of 2002 , the Monolithic Dome Institute (MDI) has been monitoring CO2 in many homes -- both domes and conventional. They all have too much CO2 most of the time. If windows are opened, CO2 levels drop to 450 parts per million (ppm)-- the same as outside. But modern houses are airtight, and Monolithic Domes are the tightest of them all. Consequently, CO2 levels can rise drastically over short periods of time.

For commercial buildings, 1200 ppm is considered the trigger point for fresh air intake. So we are assuming that 1200 ppm is the maximum we should have in our houses.

It was a surprise to us to discover (in both conventional and Monolithic Dome homes) how often we found the CO2 levels above 1200 ppm. We were shocked to find that, at times, the CO2 in some homes reached 4000 ppm. In fact we found that most homes are always above the 1200 ppm number.

The Answer

We believe we have found the answer to the CO2 issue. It comes in the form of an ERV (Energy Recovery Ventilator-- often called an HRV, Heat Recovery Ventilator). These machines bring outside "fresh" air into the home and exhaust an equal amount of the home's stale air.

And, as if by magic, ERVs also recapture most of the heat from the respective air streams. This is done in the box by an air-to-air heat exchanger. By recovering the heat, we spend less to heat or cool the exchanged air, thus saving huge amounts of energy.

In Canada, most new homes must install an ERV. Studies have led us to conclude that we should follow suit. After extensive research, MDI has found several ERV units that works very well.

Permanent Solution

On my home (Charca Casa) we a demonstrator ERV called a RecoupAerator. It is a permanent model, but we installed it in a window for closer monitoring.

As many of you know, my house consists of two, 40-foot-diameter Monolithic Domes with a central connector. Each of the domes has a 1.5 ton AC unit with internal ducting. Surprisingly, we found serious air mixing from each dome. The single unit in the living room does well for the entire house.

After we have completed our experiments, we will install an ERV permanently in the furnace space. Our experiments have shown it will work perfectly there.

My home is now always under the 1200 ppm level-- even with lots of company. We only run the ERV for a few hours each day.

As an option the RecoupAerator can have a CO2 monitor self sensing switch for automatic on or off. A second option allows manual control to actually pull in outside air at appropriate times that can by pass the exchanger and heat or cool the house.

We have recently installed an ERV in a church facility Monolithic Dome that is working very well. It has cut the air conditioning need in half.

In my opinion, every home and most commercial buildings should have an ERV.


Chew On This:

Keep in mind that there are many days when we could heat or cool the dome using just fresh air. Example: This morning it was 57 degrees outside and my air conditioner was running. It was cooling the shell a bit from yesterday's temps in the upper 80s. If we had a good way to bring in lots of air at those times, we could use it to charge the dome's thermal battery. On the other hand, we do not want outside air during an ozone alert, or when it's very humid-- even if the temperature is optimum.

At present, I'm searching for a furnace that pulls fresh air from the outside, on command, either full-flow or through an ERV. It will be controlled by a simple computer/thermostat system that can be programmed for a full range of possibilities. Properly equipped and programmed, this system could keep the air fresh while heating and cooling the Monolithic Dome as needed, using virtually no energy, for much of the year.

Updated May 16, 2008

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