[montreal]

Heat pipe is a gravity heat pump

If you wanted to have about 5 cores in series I think you would have more heat transfer, more area to defrost and more pressure drop.

More pressure drop uses more fan power. Use 100 extra watts to recover an extra 100 btu/hr. Lose on that deal.

I totally agree, unless somehow you could position the motor that drives the dual fans/blowers to be loacted in the incoming (cold) air stream, so that the electrical energy used to run the larger fans would be totally recovered. In summer, this would work against us, as we would be bringing the fan motor heat into the home, unless there could exist a switchable baffle inside the HRV to allow the fan motor to reside in a different air stream, depending on season.

Originally posted by Carnak
In reality I do not think you will get 70% APPARENT sensible efficiency when it is -25C or colder.

Obviously, when it is that cold outside that the HRV core frosts up enough that the defrost cycle comes on, the HRV stops recycling inspite of the fan motor(s) continuing to operate in loopback mode. If all the heat from the fan motor(s) is brought back into the house during the defrost mode, then I would suggest that there is no energy loss penalty during the defrost cycle. Our loss is that we only get fresh air for say 50 minutes out of each hour, not a great price to pay for the benefit of the apparatus in winter.

Where you have a point is that once we restart the HRV following a defrost cycle, new frost slowly begins to coat the interior channels well before clogging occurs and this ice film must surely reduce the heat transfer efficiency between the hot and cold side, so our 70% recovery will probably not be achieved.

 

[montreal]

I also think that with 1.2 air changes or whatever high rate you were thinking of, it will be so dry your lips will split open and you add a humidifier

Yes 1.2 ACH is high. What I have found is that as quickly as water accumulates under my evaporator coil (carrying my stale humid indoor air towards the exterior), this same water is now flowing across the floor of my AC to the base of the condensor fan where it is now being slung onto the hot condensor coils. Since there is a very strong air flow going through the condensor coil thanks to my additional 380 CFM duct booster fan located inches away, all droplets of water will be vaporized sooner or later.

Since there is no water overflowing out of the drain on the bottom of the AC, I must assume that all humidity collected by my HRV is being recycled back into the house, so there should be no net drying effect of the indoor air.

A commercial ERV will indirectly be doing the same thing since humidity as well as heat is supposed to be passing through the EVR core. But just like HRVs don't recycle all the potential heat, ERVs may not recycle all the available moisture, so an EVR running at 1.2 ACH may dry out a house faster than my freon heat pump HRV running at 1.2 ACH.

I believe I need the high rate of 1.2 ACH because that is what makes my AC operate at close to its 5200 BTU rating. The more effeciently this AC operates, the more "free" heat I get from the outdoor air, and it is this free energy that helps to offset the capital cost of purchasing my project's parts and the wear and tear on the compressor.

The professional NILAN heat pump HRV is able to operate at full efficiency with a low ACH simply because they use a TEV which guarantees optimum evaporator/condensor performance with a low air flow. My AC has no TEV, so I have no choice but to simulate the environment under which it was designed to operate at full efficiency. And that calls for adding duct booster fans in series with each flow which ultimately imposes a 1.2 ACH.

Of course I can put this device on a timer and operate it 20 minutes each hour for a net ACH of 0.4 without altering the AC's compressor efficiency. That is what I will probably do, but only when there is not a lot of heat to be "milked" out of the outdoor air in the dead of winter.

 

[Carnak]

I also think that with 1.2 air changes or whatever high rate you were thinking of, it will be so dry your lips will split open and you add a humidifier

Yes 1.2 ACH is high. What I have found is that as quickly as water accumulates under my evaporator coil (carrying my stale humid indoor air towards the exterior), this same water is now flowing across the floor of my AC to the base of the condensor fan where it is now being slung onto the hot condensor coils. Since there is a very strong air flow going through the condensor coil thanks to my additional 380 CFM duct booster fan located inches away, all droplets of water will be vaporized sooner or later.

Since there is no water overflowing out of the drain on the bottom of the AC, I must assume that all humidity collected by my HRV is being recycled back into the house, so there should be no net drying effect of the indoor air.

A commercial ERV will indirectly be doing the same thing since humidity as well as heat is supposed to be passing through the EVR core. But just like HRVs don't recycle all the potential heat, ERVs may not recycle all the available moisture, so an EVR running at 1.2 ACH may dry out a house faster than my freon heat pump HRV running at 1.2 ACH.

I believe I need the high rate of 1.2 ACH because that is what makes my AC operate at close to its 5200 BTU rating. The more effeciently this AC operates, the more "free" heat I get from the outdoor air, and it is this free energy that helps to offset the capital cost of purchasing my project's parts and the wear and tear on the compressor.

The professional NILAN heat pump HRV is able to operate at full efficiency with a low ACH simply because they use a TEV which guarantees optimum evaporator/condensor performance with a low air flow. My AC has no TEV, so I have no choice but to simulate the environment under which it was designed to operate at full efficiency. And that calls for adding duct booster fans in series with each flow which ultimately imposes a 1.2 ACH.

Of course I can put this device on a timer and operate it 20 minutes each hour for a net ACH of 0.4 without altering the AC's compressor efficiency. That is what I will probably do, but only when there is not a lot of heat to be "milked" out of the outdoor air in the dead of winter.

I misread you then, I thought that you had an HRV that could give you 1.2 ACH in the winter. I assumed you were in Quebec.

I installed a FLAIR (venmar) in an larger R2000 home in the 80s. First winter it ran wide open drying out all the moisture of construction. The next winter they installed a humidifier on their own as it was too dry. They would run that flair on low speed continuos ( guessing AT 120 CFM about 0.2 ACH) and on a rise in humidity, it would kick on to high speed at 180 CFM about 0.3 ACH. They were on a well, had a water softener, when I first saw that humdifier I laughed it was a solid block of salt.

Since then, I feel that something that can operate intermittently on a rise in humidty and give you the 0.3 ACH will be fine. The constant low speed over ventilates. Why do it on a timer, have it respond to RH.

People are their own humdifiers in the winter in a tight home. When you exhale water vapour, you are exhaling CO2 as well. Something that responds to high RH will indirecty respond to a rise in CO2.

Van EE had an optional CO2 sensor that would kick them on in intermitent mode as well.

 

[montreal]

Originally posted by Carnak

I misread you then, I thought that you had an HRV that could give you 1.2 ACH in the winter. I assumed you were in Quebec.

Actually you read correctly. My HRV is a Maytag 5200 BTU window AC reboxed to allow four 8" hoses to be connected so that each AC coil has its own inlet and outlet. I added a 380 CFM duct fan to each outlet to compensate for the resistance to air flow created by the custom made box and the lengths of 8" flexible ducts. 380 CFM will give my house 1.2 ACH, so your conclusions are based on good numbers. I also live in Quebec, so you can appreciate the climate.

Originally posted by Carnak
Since then, I feel that something that can operate intermittently on a rise in humidty and give you the 0.3 ACH will be fine. The constant low speed over ventilates. Why do it on a timer, have it respond to RH.

The reason I prefer to do it on a timer rather than on a humidistat, is I have no problem with humidity. My leaky 1979 bungalow loses a lot of moisture in winter through the walls which only have an interior vapor barrier created by sheets of Kraft paper overlapped and stapled every 2 feet. The exterior air barrier is created by rolls of 3 feet wide black building paper overlapped by a few inches.

My main problem is the stuffyness of the inside air due to abundant use of carpeting and flakeboard sub-flooring. So ventilation has more to do with getting rid of odor rather than excess humidity. In winter, RH falls to about 30% and there is still a slight film of moisture on the windows.

 

[Carnak]

man, you got me hook line and sinker. That you eddy?

 

[davidr]

man, you got me hook line and sinker. That you eddy?

Was thinking the same thing. LOL!

 

[montreal]

man, you got me hook line and sinker. That you eddy?

Was thinking the same thing. LOL!

If you're referring to me, I'm not Eddy.

You can call me Al.

 

[deejoe]

Hey Al, er, I mean Montreal. you say in the winter your RH is only 30%....???? why on earth would you ever need an Hrv, especially this glorified a/c untit with a heat asorbing core.
Puzzled in Ontario, Central that is.

 

[montreal]

you say in the winter your RH is only 30%....???? why on earth would you ever need an HRV, especially this glorified a/c unit with a heat asorbing core.

The simple reason is we leave the windows closed most of the year, either because we have armed the alarm system while away, or because the nearby expressway is making too much noise during the week.

Two thirds of our 900 sq feet bungalow has 15 year old carpeting over a foam underlay made from foam pellets glued together to form sheets. Under that underlay is three quarter inch flakeboard containing lots of formaldehyde glue.

Even with the central furnace fan running 24/7, whenever we entered our house after having been outdoors for several hours, we were hit by the internal odor due to all the products I mentioned. After a few minutes, our noses quickly got used to the odor and we were unconscious of it.

Ironically, I can walk into condos built with concrete floors and walls and hardwood parkette flooring, but with no mechanical assisted ventilation, and not detect any odor there. So wood framed, carpetted homes may have a character all to themselves.

The price for having all our carpetting replaced with hardwood flooring would cost about $6000. Until then, we depend on some form of assisted mechanical ventilation to constantly introduce fresh air into the house.

In winter, the odor is never as strong as in summer. My primitive system operated only in the summer from 1993 to 2004. When my wife arrived in 2004, she wanted to work at home year round and I converted my original ventilation system into an AC system, but I had to give up the fresh air exchange because I only had so many 8" diameter holes in my basement wall and we needed them all for the DIY AC system. There's another thread devoted to that unique installation. Search my username to read all about that.

This year I decided that it was time to re-introduce a fresh air exchange system again, but on a year round basis. When the computer model showed that 0.4 ACH was going to cost $225 per winter in increased heating costs, I decided to realize a 20 old dream of mine - replicate a Nilan VPL-15 HRV using a $100 Maytag window air conditioner.

Right now, as I am writing this post, it is 55 degrees F outside. My HRV is taking 75 degree air from the kitchen and bathroom and cooling it down to 52.2 degrees before sending it outside through new holes I have made in the basement wall (actually in window inserts). It is taking the exterior air of 55 degrees and heating it up to 99.9 degrees. The device is drawing 5.3 amps and probably consuming about 400 watts because of the bad power factor. 350 of these watts is coming back into the house because the compressor and two fans (of three) are located in the incoming air flow.

Let us suppose I replaced my compressor with a 300 watt light bulb. Perhaps my incoming air would end up heated from 55 degrees to say 65 degrees due to the 400 watts of passive heating. So if I am getting 99.9 degrees by using a freon compressor which also draws 300 watts instead of a 300 watt lightbulb, then I have picked up 35 degrees for free with the only penality being the 24/7 wear and tear (in winter only) on the $100 AC from Home Depot.

At 7 cents a kilowatt hour in energy savings for my electric furnace, how long will it take for this "free" heat to pay for a replacement AC when the Maytag wears out?


Once the replacement AC is pre-paid for, any additional savings will be applied against the new $225 per winter cost that is occurring now due to the air changes created by this new HRV.

[Edited by montreal on 10-01-2006 at 11:36 AM]