Hot water to forced air

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On Jan 4, 10:59 pm, snipped-for-privacy@snyder.on.ca wrote:

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The unit has a slot for an electrotatic airfilter that is not being used, my son plans on test various designs by building them so the will slide in place of the filter. He may well be able to find a radiator that would fit. He was talking about taking a look at the heater core out of a school bus one day this week to see how it may fit.
Jimmie
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On Wed, 4 Jan 2012 20:23:41 -0800 (PST), "hr(bob) snipped-for-privacy@att.net"

And heater cores are LOWER RESTRICTION than rads - at least if you get the right one. 2 big heater cores will work inplace of a radiator in many cases - lots of aircraft flying (home-built) with 2 heater cores or 2 air conditioning evaporators instead of a rad.
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The OP may be well served, to set up a separate hot water heat system. I knew some folks who used a car radiator and a fan indoors. Outdoors they had a wood stove with pipe loop inside the stove. Hot and return pipes under ground, and circulating pump. One of a kind, the people and the heater.
Christopher A. Young Learn more about Jesus www.lds.org .
I did the reverse of that using cold groundwater to help cooling in the summer. I used an old automobile radiator placed in the air stream in addition to an A-coil that was part of a regular central cookling system. I don't see why the OP couldn't try an auto radiator and save a lot of $$$ over buying something else.
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Personally, I'd go at it a little differently. Since this solar assist is not the PRIMARY heat source, I'd install the solar hydronic loop in the RETURN air to the furnace - and to avoid excessive restriction I would put it in PARALLEL with the existing return air duct . Properly designed, the heat exchanger could have very little more restriction than the open return, and a system of dampers could restrict the airflow on either side to extract the maximum heat from the solar loop.
Because the delta T is higher on the return side than on the heated side, you would get more heat ( in absolute BTUs) out of the solar assist than if it was being used on the outlet side.
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On Jan 4, 9:15 pm, snipped-for-privacy@snyder.on.ca wrote:

I think the OP is already planning on putting it on the return side. He said he had a filter unit that was not being used and he could put the heat exchanger there. On the return side is the only place that makes sense to me.
- and to avoid excessive restriction I

You'd always get maximum heat extraction with the most airflow through the heat exchanger, so why the need for a system of dampers to vary the flow?

Agree, which is why I don't think it makes any sense to put it anywhere else. But first thing I'd do is figure out how many BTUs of heat are really available on a typical day. And he could only expect to recover some portion of those, clearly nowhere near 100%. Having some numbers he'd have an idea if it would be worth it.
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wrote:

Return could work, provided the Btus are there AND the air leaving the water-to-air heat exchanger is always above the return air temperature AND below the AHU supply temperature.
If at any time the water is cool, it will cool the return air and make your heat pump or furnace run more. If at any time the water is hot, it will overheat the space while the heat pump sits idle.
Whereas if you put the heat at the heat pump, the builtin controls will take care of all that for you.
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wrote:

. Which is why I recommended an "air blend" system using a bypass and dampers.

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On Jan 5, 8:24 pm, snipped-for-privacy@snyder.on.ca wrote:

Sure. That'll work fine, in the average residential computer controlled environment.
Gonna use PID control on those dampers, or something more sophisticated, one of the new fuzzy logic systems maybe?
Most of what you and the others propose adds complexity and advanced control requirements. I'm trying to suggest going upstream of existing controls to take advantage of what's already there?
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wrote:

Depending where he lives, the solar assist could extend the "no heat required" season and reduce the heat required through the winter.
Not likely to help much in places like Halifax or Seatle, but could conseiveably produce pretty good winter results in Regina or Winipeg, or other places with long hours of winter sunlight.
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Actually there is a lot of solar energy available in the winter. My Sun room walls are made almost totally of sliding glass doors. Glass is open during warm weather closed during the cold. Jimmie
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Are you trying to tell us you can get more heat out of the same radiator system with less air flowing through it instead of more? How do you maximize the temperature difference if not by using the maximum available air flow? Hmmm?? Air barely moving results in the air being hotter in the heat exchanger and less energy transfer. Air quickly moving results in the air being cooler and more energy transferred. Do they put part of the air through a furnace heat exchanger, or ALL of it? Do they put part of the air through an HVAC evaporator or all of it?
Turbulence does increase the transfer. You think you're gonna get more turbuluence with reduced airflow? Ever hear of a Reynolds number?

He isn't designing the heat exchanger. It's a simple radiator. You want to make it into PHD thesis?

Uhhuh. And one way to get it as high as possible is for the max airflow of the furnace to be going through the radiator. Anything less than that for the same design and he gets less heat transferred.
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Unfortunately it doesn't work that way. You want the water temp of the water leaving the radiator in the air stream to be as low as possible. That way it can pick up the most new heat on it's pass through the solar collector.

I agree that unless it's a very large solar collector it isn't going to meet the demand. But for it to work at all he needs a radiator of sufficient size. If the water isn't giving up most of the heat collected into the air stream via the radiator, he just winds up moving hot water around and getting little heat out of it.
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On Fri, 6 Jan 2012 05:55:31 -0800 (PST), " snipped-for-privacy@optonline.net"

Mabee we need to get a bit more "scientific" about it. You want to put as many BTUs of heat (using north american (canadian)n terminology) into the air from the water. A BTU is the amoiunt of heat energy involved in cahanging i pound of water 1 degree F. Water weighs 10 lbs per imperial gallon. (works better than 8.35 per US gallon for calculations).
Lets say we have a 40 gallon reservoir of water at 127 degrees F and we pump it through a heat exchanger at a rate that reduces the temperature of the water returning to the reservoir to 87 degrees F.. That means we got 1600 BTUs of heat out of the water, into the air.
To do that in 1 hour would require a water flow of 40 gallons per hour, or .66 gallons per minute.
If the return air is at 68 degrees F, and the furnace fan moves 2000 cfm, what will the air temperature coming out of the heat exchanger be?
1 BTU will raise the temperature of 1 cu ft of air 55 degrees F, or 55 cu ft of air 1 degree F.
So to absorb 1600 BTUs of heat from the water into the air, we need (1600x55=) 88000 cu ft of air raised one degree F, so at 2000 cfm, or 120000cfh, we would on,y raise the temperature by 0.73 degrees F.
If we drop the water temperatre leaving the exchanger at 77 degrees, the air would be raised by 0.91 degrees F.
SO the variables that ALL make a difference are the airflow, the waterflow, the temperature drop across the water side of the exchanger, and the desired outlet air temperature.
If you balance the water flow against the air flow you can make your delta T between the water and the air whatever you want it to be. - which is where a BYPASS system as I explained, allows you to get the results you want by varying the amount of air passing the exchanger and the water flow through the exchanger once you get the basic size of the exchanger close. A bus heater core could be 25000 BTUs.
Many car heaters are about 12000 BTU at 140CFM - but we do not know what the design temperature drop is across the exchanger. The delta T would vary depending on the inside temperature.
A 10X10X2 heater core, at 170CFM, is rated at 20,000BTU. Again, we do not know the design temperature drop, or at what air temperature (delta T)
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On Jan 6, 4:58 pm, snipped-for-privacy@snyder.on.ca wrote:

Why the need for variable dampers? Do you disagree that you get the most heat out of the heat exchanger by moving all the furnace air through it?
The only reason I see for using less than all the airflow is because without severly restricting the airflow, the air coming out is going to be almost the same temp as the return air coming in. So, to avoid draft/comfort issues, you might want it to come out warmer. BUT, and this is a big but, if that is the goal, then you'd have to change the blower because even at the lowest blower speed I doubt any system he's gonna put together is going to raise the air temp more than a deg or so. And I don't think you're proposing that he just damper off a huge portion of the existing airflow, leave the blower as is, are you?
That's why I dismissed using just solar from the beginning and I assumed he was talking about using it to supplement the furnace heating only when the furnace was running. If he wants to run the system all day long, using solar, that gets into a whole additional list of potential drawbacks, many of which I believe would make it impractical.
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On Sat, 7 Jan 2012 06:37:46 -0800 (PST), " snipped-for-privacy@optonline.net"

No I'm not disagreeing. IF using a "bypass" system the dampers would take the "bypass" out of the system when there is no appreciable heat to be gained from the system, allowing the solar panels to get the water hotter so the delta T would be higher, raising the efficiency - and therefore extracting more heat from the system..
Same thing could be accomplished by a set of water control valves tho keep the heat in the reservoir untill the temperature was high enough to do an efficient job of heating the interior of the house. Water valving is more complex, and the difference in efficiency re: switching water vs switching air, would be small enough to not make the complexity worth while. Shutting off the air flow through the secondary heat exchanger MIGHT increase the efficiency enough to make it worth while. It would also eliminate the problem of extracting heat FROM the return air, into the water, when the solar input was too low to provide a net heat gain.
Can't do that without water controls in a non-bypass system.
I'm NOT saying this method would necessarily be BETTER for the OP, but it definitely bears looking into for the reasons given.
Recap:
No additional restriction in the main ductwork. Smaller heat echanger could possibly be employed Less complicated water controls Possibly higher total efficiency.
Add to this, the installation might be simpler - just 2 cut - ins to the return duct (or even just one if the "bypass" augments the cold air return from heated airspace) - and for an "experimental system" it makes implementation a lot easier and more easily reversible. A simple "zone damper" like a Famco POPC or Suncourt 8 inch motorized unit , at about $70 would do the job., but a modulating unit like the Alan AZRDMOD series would provide variable control if desired, for more like $200.

Nope. That's why I call it a "bypass" Instead of restricting total airflow, I am advocating he SUPPLEMENT the airflow

Add a duct blower , like a Fantech FR225 - about 450-500 cfm for 8 inch "bypass" duct.

It would require having the circulating fan on "constant" which I do all year, just as a matter of course, for filtering and comfort purposes. So, at least for me - not a drawback.
As my 28/40KBTU furnace only runs 8 hours a day on the COLDEST days here in Ontario, and averages closer to 6 hours on low fire - I only need a total of 168000 btu heat input to keep the house comfortable..
If I have 6 hours of useable sunlight, a solar assist system could conceivably provide well over 10% of my heating needs throughout the winter, and a lot more heat, and a much higher percentage, during the "knee seasons" when more sun is available and less heat required.
The payback would still be SLOW - my total annual gas bill for heat and hot water is about $700 per year - - - but the house would be more comfortable in the early fall before I turn on the furnace, and late spring, when I shut it off.
The OP isn't the only one who's considered it - but I'd need to provide the solar panels too - which he already has.
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On Jan 7, 3:45 pm, snipped-for-privacy@snyder.on.ca wrote:

That's good. I guess that leaves harry all to himself.

You have the same situation with the solar collectors as you do with the radiator. Slowing the water flow or air flow isn't going to get you more heat or improve the efficiency.

What reservoir? It would have to be one hell of a reservoir to make any difference in heating the house. I think it's simple. Either on a decent sunny day you get enough energy out of the solar panels to make it worthwhile to fire the' blower up or not. Once it starts it's probably gonna run most of the time, even on days where you just need a little heat. On colder days the furnace will have to come on too.
 Water

Smaller than what? How are you going to heat a house with a smaller heat exchanger? For it to work, I'd say he's going to need as large a one as he can fit practically, or pay for, etc.

Yeah, we;ve been down that path before. And you know my opinion, which is circulating air all the time in most cases is an energy losing proposition. Look at the typical duct work. In my house for example, I have long runs that go 50ft through an unfinished basement, then up two stories through outside walls. The last thing I want to do is be moving air through them where it can lose energy 24/7.
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On Sat, 7 Jan 2012 13:31:04 -0800 (PST), " snipped-for-privacy@optonline.net"

How big does he need ? A standard tube and shell heat echanger can be good for 50,000 to 60,000 BTU per square foot.. A smaller exchanger with higher air velocity can be every bit as good as a large one with low air velocity - and being "off line" or "parallel" has NO EFFECT on the duct resistance.

Well, around HERE, nobody in their right mind rund heating ducts in outside walls. And with the cost of housing, unfinished, unheated basements are an almost unheard-of "luxury".
Hardly call your house "typical" here. In MY house, themain "trunk" hot air duct runs through the laundry-room /wife's office, exposed on the bottom to the room, and the top to the main floor above - with accoustic tile ceiling. The heat ducts to the upper floor runs through the center load-bearing wall, and the ductwork to the main floor registers run between the floor joists between the main floor decking and the accoustic tile ceiling of the rec room / my office and the laundry room/ wife's office.
The one stupid thing they DID do is running the water lines to the upstairs bathroom up the outer wall from the main floor bath.
My house is VERY TYPICAL of housing in my area - circa 1970 - and most are built even more efficient today. Most houses built here since the mid to late 40s are built in a similar fashion
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wrote:

No, it just shows that this house is far more advanced than Traders - which runs the heat pipes up the outside wall and has an unheated basement.
How is your Euro-shack any better than mine?
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wrote:

We have places like that here too. But they are not "typical" here - or there. Ond on the whole, American, and particularly Canadian homes are more energy efficient than the average British dwelling, by a fair amount.

What is the normal R value in the walls and roof of the average new british house? What is required by "code".
How much gas does it take to heat a 1300 sq foot home in the coldest part of Britain (which is still, on the whole, not as cold as most of Canada)???

They build differently in the USA than we do up here in the "great white north". 6 inch walls with strayed foam insulation are not out of the ordinary here any more. The house my father built 30 years ago was heated by 1/2 cord of wood per winter- and it was a "conventional" urban split level of over 2000 square feet.

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wrote:

I heat my "snow belt" Ontario home for $700 worth of natural gas a year - which also provides all my domestic hot water.
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