Energy Loss From Heating & Cooling

It’s all about the air

Building super tight to prevent heat loss, keeping the air conditioned space comfortable, and keeping occupants healthy all require us to take a good look at the air inside our house and how it is conditioned.

A few things seem apparent: It takes a lot of energy to heat or cool the air inside our homes to make them comfortable. This is especially true for many of us who live in the cold northern states, and also true for those living in hot climates that need a serious amount of air conditioning. The biggest running expense of our house is keeping it heated and cooled to a comfortable temperature. Most of the energy losses in our homes comes from air leaks. These can be unintentional leaks thru wall structures, from the roof, thru the flooring, around windows, doors, wall penetration points such as those for plumbing, electrical, and other utilities, as well as air that is directly pumped out thru intentional “exhaust” vents commonly found in baths, kitchens, dryers to name a few.

( Image: Albemarle heating)

Air quality inside homes is rated to be 2-5 times worse than outdoor air. If you think about the amount of harmful emissions that can become trapped inside a home, this starts to make sense. For example, car exhaust from the garage that does not get out before the garage door is closed. Seems to dissipate over time, but those chemical simply diffuse thru a large amount of air including that air entering the living space when the adjoining door is traversed. Fumes from gasoline powered lawn tools, paint cans, and other chemicals, cleaners, sprays of various types used during the course of daily activities, musty air from basements, possibly radon, and molds that slowly spread throughout our homes. Although our home are “leaky” and air and heat are being lost at all times, some of these harmful toxins unfortunately remain trapped at high levels in the home.

Based on what we have seen so far, here is what we are considering as an efficient and reasonably realistic solution. There are several key points:

We want to aim for first creating a super air-tight building envelope:
The structure of the house itself should be as airtight as we can possibly achieve ( within a given budget, offcourse). The basic idea is simple: don't lose conditioned air and thereby reduce energy losses in the first place. Europeans seem to be far ahead of us in this regard with their PassivHaus standards that require a house to meet a blower test which puts the house under a negative pressure to check for air leaks. If the house exceeds air leakage of 0.6 air changes per hour, it fails. An airtight building shell that meets 0.6 ACH @ 50 pascal pressure is the official requirement. We want to aim for meeting or exceeding this level of air tightness.

We want to maximize air quality:
With the air sealed within the home, it will eventually become horribly stale from use, and those chemicals and toxins will be trapped even more than before. We will achieved energy savings but the house will become unlivable. We will need to exhaust the stale air out and bring fresh air in. We know what you are thinking.. that puts us right back where we started: exhausting heated air out and bringing cold air in. But fortunately, this issue has finally started getting some attention and we are seeing devices on the market that can exchange the heat from the stale indoor air to the fresh incoming air before throwing it out of the building. These Energy Recovery Ventilators (ERV’s) and Heat Recovery Ventilators (HRV’s ) are becoming readily available and more and more efficient each year. Infact some companies are claiming efficiency of heat exchange above 90% which seems almost too good to be true. We will look deeper at these as we get further along in our projects, but for now the idea of an ERV seems like it will be a crucial part of our energy and air quality management system.

To get back to our original concern, why go thru all the trouble of sealing a house, only to end up having to ventilate it again? Well, there are significant advantages to controlling precisely how, when, where, and what amount of air enters and leaves the home. Assuming the ERV’s are able to recover 90%+ of the heat in the exhaust air, we can efficiently pump the whole house’s air out and bring fresh air in at a slow controlled pace around the clock! Not only that, we can filter the air coming in to further clean it of allergens, road dust, etc. We can also position the air intake at a location to minimize sucking in lawn chemicals at low ground levels, bugs, etc. This approach is consistent with our general belief that it is better to eliminate the source of a problem rather then trying to compensate for it later. Keep unwanted pollutants and bugs out, and you will need less cleaners, and pesticides inside the home later: +1 for indoor air quality.

We want to eliminate as many heat wasters as possible:
Bath vents, kitchen vents, laundry vents, etc intentionally take heated or cooled air and pump it out of our homes at very high volumes. These all seem necessary at first glance, but we are looking for successful examples of creative air planning that can be used to eliminate the energy losses from these systems while achieving the same functionality. The bath vents are the easiest to address. We are thinking of piping these directly to ERV instead. No bath vents at all, instead a 24 hour exhaust of bath air direct to the ERV! This will be at a slow pace, barely perceptible and without that aggravating fan noise of a typical bath fan. The bathrooms will thus be continuously vented not just when in use. In addition, it is possible to add a timed booster switch in place of the normal bath fan switch. When a user flips the booster switch, the ERV system goes into a high speed mode that increases its air speeds for a timed period ( usually about 15 minutes) and then automatically goes back to its slower rate. The user does not need to learn anything new, and the system takes care of everything behind the scenes. The heat from all of the air exiting the baths, is transferred to an equal volume of fresh air drawn into the home.

The kitchen and dryer are more challenging:
We believe the following will work, but have to do more research before we are ready to commit to this solution. First, we are planning a high quality charcoal filtered recirculating hood over the cooktop. It will trap most of the grease, and odors directly above the cooking area. But the air will not leave the room and just be blown back into the room. Generally we dislike this approach in the past, but here’s how we take it to the next level. We will place one or two air intakes to the ERV in the kitchen as well. We have to keep these atleast 10’ away from the cooking area because the ERV cannot handle the grease. If we place the intake far enough away, we eliminate the grease issue, but can still pull odors from the kitchen air on a constant basis while recouping the heat from that air. An additional booster switch in the kitchen allow us to push the system into high speed mode when necessary and otherwise let it run 24hours a day at a slow speed. Ultimately this would result in far more fresh air into the kitchen than a conventional direct outside venting hood can provide. Not only that, the whole house would be continuously purged of stale air, and odors would not linger for long.

Lastly the dryer. Again, the ERV will not play well with the lint from the dryer. We are not seeing any good solutions for this one yet. The best we have come across so far is to use a heat pump dryer instead of a conventional one. These are super efficient and do not need a vent, however it seems to be technology that europeans have had for years and we don’t. It’s sad how we are so far behind in this country on technology that is readily available in other countries. Hopefully our efforts can help change some of that. We will look into this further as we progress and see if we can integrate a ventless dryer at a cost that doesn’t break our budget.

We want to hear from you. Share your ideas on how we can take indoor air quality to the next level by minimizing energy losses while maximizing fresh air.