Heat Recovery Ventilation | <– Date –> <– Thread –> |
From: Roger Diggle (digglemacline.com) | |
Date: Thu, 3 Nov 94 02:56 CST |
> Roger: Please send the info on air to air heat exchangers. > We are very interested, having first heard of them > while reading about the Toronto GreenHome. > Thanks, > Stephen Hawthorne > Blue Heron Farm > Chatham County, NC Modern construction practices allow for the construction of very airtight houses. The average thirty year old house is leaky enough to provide several air changes or more an hour if it's very breezy outside. This is good, because it removes contaminants from the house, but it's bad because it causes a direct heat loss when the air you paid to heat leaks out and is replaced by the 20 degree air that comes in through every crack and crevice. It also produces draftiness, which causes discomfort and increases the temptation to walk over to the thermostat and do the wrong thing. In a tight house with no ventilation, on the other hand, the humidity will rise to levels uncomfortable for the occupants and insafe for the structure and personal belongings. Double-glazed windows will fog over and wallpaper will peel. Other contaminants will also concentrate. In tight construction, in most of the country, the amount of ventilation required to remove the excess moisture will generally reduce any other concentrations to acceptable levels (though not always). The nice thing about air-to-air heat exchangers in tight construction is that they allow *you* to control the amount of air exchanged, rather than depending on outdoor airspeed to do as it will. Air-to-air heat exchangers, or, as the industry seems to want to call them these daze, heat recovery ventilators, get rid of excess moisture and other indoor air contaminants and provide replacement air that's as fresh and clean as your outdoors. Some of the air from your house is blown through a heat exchanger and then to the outside, carrying nasties with it. Outside air is blown through the heat exchanger and into the house, picking up much of the "waste" heat from the air you are throwing away. They generally have four duct connections: two for the air you're getting rid of and two for the fresh air you're bringing in. The air to be removed is usually removed from the bathroom and/or kitchen, and replaced in the main living area, or blown into the furnace ductwork, if such exists. Several companies make this equipment. I'll fish for information about more of what's around, but here's a run down of what I know at this point: Altech Energy's design is based on a heat exchanger manufactured by Mitsubishi, I think (some Japanese company), of a special moisture permeable paper. Because of the permeability, no defrosting is required, a plus, but longer run times are necessary to get rid of a given amount of moisture, a minus. They also offer an impermeable heat exchanger core (polyethylene, I think) that would not be appropriate for Northern winter weather. Overall, I think their design is superior to most others. The heat exchanger core itself, and the design of the ventilator it is used in, are both very elegant. The only mechanical things are the single blower motor that operates both blower wheels, and the humidity control that turns the unit on and off. Altech also offers a recovery ventilator that installs just about like a bathroom fan, and would move adequate air for a small tight dwelling. It's even available with an energy efficient compact fluorescent lamp built in. Altech Energy (608) 221-4499 7009 Raywood Rd Madison, WI Research Products has dealers all over creation... many heating / air conditioning / refrigeration supply houses handle the line. Their air-to-air is a very new product, however (about a year, I think) and may suffer in some places from unfamiliarity. This company has made very good humidifiers and high-efficiency air filters for many years. Research Products' ventilator design (the mechanical layout) is virtually identical to Altech Energy's, although it's a bit nicer looking and has some advantages in ease of installation. Many years of manufacturing experience pay off. They can't use the patented Mitsubishi heat exchanger, however, so they came up with their own exchanger design, also made of moisture permeable paper. The design doesn't seem as elegant, but may in fact work just as well. Research products also makes a very nice humidity control that automatically readjusts it's setpoint with changes in outdoor air temperature. Very nicely done, and reasonably priced for what it does. There are other schemes for controlling the ventilators, such as timers or manually operated switches, but I think that humidity control is the best method, especially with a control like this that can reset itself according to outdoor temperature. If the ventilator could be sized just right, I suppose that it could run full time, but that has disadvantages as well. Research Products (608) 257-8801 1015 E. Washington Ave. Madison, WI 53703 The other two basic designs I'm aware of use either moisture impermeable heat exchangers, usually aluminum, which are generally larger and require defrost controls, or "heat wheels" which use a rotating heat exchanger. The heat wheel exchanger surface, usually a fine, open-ended honeycomb, rotates through the exhaust air stream collecting heat as the air passes through it. It then continues rotating through the intake airstream, giving up the heat it collected to the incoming fresh air. They should be self defrosting. This is a design that has been used in commercial buildings for some years, so it isn't as contrapted as it might sound. Mechanical parts involved are blower motor(s) and a motor to rotate the heat wheel. Drain lines would be required to get rid of the defrost water. Honeywell (Minneapolis) and Carnes (Verona, WI), among others, use this design. Carnes's unit had something of a reputation for mechanical trouble in the past, but the problems may be resolved. It's been around a while. I'll try to get some scuttlebutt on it. Honeywell's unit is a fairly recent entrant, I think about a year or so ago. Honeywell typically makes good stuff, though I have no experience with this unit other than a peek at one at a supply house. All the moisture impermeable exchanger models I'm personally familiar with are large, commercial size, for large buildings, swimming pools and other specialty applications. I'm not personally familiar with any of the models manufactured for residential use, though I'd guess that the largest number of manufacturers use this design. These exchanger cores will frost up in cold weather, and, if not defrosted, will lose exchange efficiency, and eventually become completely ice-blocked. The defrost controls typically involve timers and/or pressure controls that operate dampers to close off or bypass the cold incoming airstream around the exchanger core, and use the warm discharge air to melt the ice. This extra stuff is in addition to the humidity control that operates the unit in the first place and the blower motor(s) that move the air. It's also necessary to provide drain lines to get rid of the water. It makes for a more complicated ventilator. That's why I like the moisture permeable core designs the best. One other possible unit to check into is a Therma-Stor unit that combines heat recovery ventilator with heat pump and water heater. I've only seen literature, not the equipment, but I've worked with their combo heat pump / water heaters a few times, and they seemed to be pretty well thought out. Therma-Stor is also, amazingly enough, in Madison... A division of Dairy Equipment Company. Therma-Stor Products Group (608) 222-5301 2001 S. Stoughton Rd Madison, WI Hope this helps... Roger Diggle - via BulkRate 2.0 *********************************************************************** Mac Line BBS: (608) 233-9487 - A FirstClass System in Madison, WI USA **********************************************************************
- (no other messages in thread)
Results generated by Tiger Technologies Web hosting using MHonArc.