Ask Jon Eakes

Last Updated: Friday, October 15th, 1999, Created: Friday, October 15th, 1999

ARE HEAT RECOVERY VENTILATORS (HRV's) WORTHWHILE?

You should understand clearly that air-to-air heat exchangers, or Heat Recovery Ventilators (HRV) as we know them in North America are really two things rolled into one: Balanced Air-Change Systems with the added feature of Heat Recuperation. The exhaust and supply ducting and fans are subject to all of the comments in the previous section. The question to really consider here is whether the addition of heat recuperation is worthwhile.

Most heat recuperation claims of manufacturers of 80% to 95% efficiency are actually exaggerated as they relate to ideal conditions and not real seasonal efficiency: different fan speeds, wind interference, frost obstruction, defrost down time, maintenance and cleaning down time. I believe that a 60% to 70% real seasonal efficiency is a fair evaluation for all the current models. Further it should be realized that we are not trying to recuperate 70% of the vast quantities of heat we used to loose from our drafty old houses, but rather 70% of the heat exhausted with the minimum ventilation we allow in our newly sealed houses. That 70% of a much smaller pie. In essence we recuperate less money than we might like to think. One Swedish study shows real savings of only $60 to $100 a year.

Next we must evaluate how much the hardware (and maintenance) for this heat recuperation costs over and above an equivalent balanced air-change system without heat recuperation.

If you use the keyword "Financial" to locate the title "HOW DO YOU CALCULATE COST PAYBACK?" you will get some perspectives on how to compare the costs with the benefits. With today's capital costs and moderate seasonal efficiencies it takes a very cold climate (a lot of heat to be added to the fresh ventilation air) to justify the expenditure. Although local calculations should really be made, you will find it is easy to justify the cost of an HRV in regions above 5,000 Degree Days Celsius and hard to justify it in regions below 4,000 Degree Days Celsius. (Use the keyword "Degree Day" to locate the " Canada Degree Day Map") All the rest of you in-between will just have to sharpen your own pencils.

Keywords: Air Quality, Environmental, Exhaust Fans, Fans, Hrv, Ventilation

Print Send To A Friend

Article 738

Privacy | Ruby on Rails Development by Isnor Creative