Have you ever put together a jigsaw puzzle and spent HOURS getting it all together only to find that you are missing a piece when you are about to finish. Oh sure, we’ve all checked the floor under the table and chairs, looked under the couch because we just know we kicked it under there, and even given Rover the evil eye. Sometimes we luck out and find it, and sometimes we don’t. But what if we didn’t know we lost a piece until a lot of time had passed and suddenly our beautiful puzzle is getting moldy, and we are constantly sick with something?
In the 1970’s we thought we knew just what was needed – air tight construction, the tighter the better… until the problems started. By then the bloom was off the rose and the public didn’t want to hear about a fix. Too many issues of mold developing or talk of cancer from urea formaldehyde turned a lot of consumers off of the new energy saving schemes, though they liked those new fangled double paned windows. Those made sense and they were familiar, plus you could tell you were warmer once they were installed.
While America’s interest in highly energy efficient buildings waned, Europe picked up the ball and ran with it. They figured out the missing puzzle piece – controlled ventilation. The buildings needed to breathe, but the heat needed to stay inside or they wouldn’t be energy efficient. The technology behind heat recovery ventilators was improved to the point where the missing piece fell into place.
The Passive House Institute worked out the requirements that heat recovery ventilators must meet to be PHI certified and planned for the air quality in the buildings based on use and occupancy. The PHPP includes these measurements in the Ventilation worksheet. This is where you will make sure you planned enough fresh air for the project and list which HRV or ERV you are using.
For those who are just a little fuzzy on the concept of Heat Recovery, I like to use the analogy of a sprinter who comes in with the fresh air and is holding the heat baton, running around your house until he is exhausted, and just before he leaves he passes the heat baton to the incoming fresh air sprinter. Because one of the properties of heat is to go towards cold, the HRV manufacturers figured out a way to let the incoming air chamber share a common heat transferring material wall with the exhausting air so the heat would head to the colder side to warm the incoming air while the stale air without most of its heat was exhausted.
The Ventilation worksheet needs you to describe what kind of areas will need special ventilation requirements such as a kitchen or a bathroom. There are spaces provided for additional rooms should you have other ventilation needs that aren’t listed. Below that section is one where you will choose the hours a day that the building can expect to be occupied and to what level. Perhaps you work at home and are in the house quite a bit, that would require one level of air supply. What if you worked long hours away from home and were only there part of the day? That would require a different set of air supply considerations. Fortunately the PHPP does recognize that people do use their buildings differently and allows you the ability to say you use it heavily for 50% of the time and lightly for the other 50% or even split the usage further – just remember though, there are still only 24 hours in a day, so make sure you cover all of them and no more! <grin>
Because the air pressure a house faces can affect its performance, the PHPP needs to know if there are buildings or other structures that would screen your project from direct wind gusts. The Ventilation Worksheet is also where you will list your blower door test results.
The fresh air and exhaust air needs to be balanced and the runs of the ventilation system should be kept as short as possible. Care needs to be given to insulating the incoming air ducts so that you do not have condensation issues and the length of these ducts and the amount of insulation used is entered into the PHPP as well as where the HRV is located (within or outside the thermal envelope).
Some people like the idea of using a subsoil heat exchanger to help with the pre-heating of their incoming fresh air. There is a spot on the Ventilation worksheet for recording that and a note that refers you to additional information available from the PHI website.
Finally you will list the HRV or ERV for your project. If your unit has not been certified by PHI, they will take 12% efficiency off of any accredited score the unit has. They do this because sometimes the reported manufacturing figures are a bit elevated because of ideal test conditions, and not real world conditions. Experience has shown that 12% is a reasonable amount to use as a correction factor.
Now the pieces of the puzzle are falling into place. The PHPP makes sure the critical missing element is well considered so that the mistakes of the ‘70’s are not repeated.
Up next – Annual Heat Demand and the Monthly Method.