Home Heat Exchanger

Suck it and see.

It would improve its chances if all the normal economy improvements were in place in the home:

• Draught excluder strip on all doors and windows
• Loft insulation in excess of current Building Regulations
• Double glazing (triple-glazing is common in Switzerland)
• Cavity wall insulation
• Reflectors behind the radiators
• Thermostatic radiator control valves
• Room thermostat(s)
• Recuperation on the furnace stack
• Insulation on the furnace and its supply pipes leading to and from the house
• etc.

It is possible to heat a home on only 100W if the insulation quality is high.

What about ground-source heat pumps with a coefficient of performance around 2.5?

What about solar gains - can that conservatory be put to use as a warm air source?

I sure wish 100W was all we require here in Canada. I have 90 % of my heat in use, right down to the drain water and I can't heat that cheap. The house is so well insulated I can cool it in the summer to 20c with a 5200BTU unit and it then only runs 6 out of 24 hours.

My stack for my furnace is so cool that I have to trap the moisture before it goes into the flue. All that goes up is gases, CO2.

I don't think you'll have a problem. If the h/ex is rated 350,000 BTU with the temperatures stated - average 170°F on hot side, average 110°F on cold side, ΔT 170 - 110 = 60°F (without going into log mean ΔT, to keep it simple).

As the actual heat transfer is ~ 200,000 BTU, actual ΔT = 60*200/350 = 35°F. So the radiator side of the h/ex will have average 170 - 35 = 135°F, in/out temperatures 125/145°F.

Cheers.......Codey

Is this a homework question?

Hi: Here are some thoughts from an old Hydronic Heating service man. As I look at the numbers that you have provided you may have problems heating your home in very cold weather.

The normal water temperature design for baseboard radiation is supply water temperature 180 degrees F and a return water temperature of 160 degrees F. When the boiler is fired to the maximum capacity of 220,000 Btuh I would expect to see the water temperature entering your baseboard radiation to be in the area 135 to 140 degrees F. This would mean the capacity of your baseboard radiation would be de-rated by aproximatly 30%. This new capacity may not be sufficient to heat your home in cold weather.

I would suggest that you obtain the performance specifications for this heat exchange when the heat source is 220,000 Btuh. This information should give you a new output Btuh capacity for the heat-exchanger.

You should recalculate the capacity of your existing baseboard radiation based on the lower heat source water temperatures.

I would also suggest that you have a very detailed heat-loss done on your home. You may find that you have sufficient over capacity in your currant baseboard heating system ??to heat your house. If not you will need to add some radiation or a secondary heat source to cover the short fall.

I hope this helps.

It depends on the assumptions. The OP has said heat demand is 200,000 BTUh which we have to accept as accurate or we're talking about a different problem. Also that the radiant side of the exchanger is rated at 120°F. and return at 100°F. Is the heat output ~ 200,000 BTUh at these flow/return temps? If so there is no problem.

Then there is the 350,000 BTUh heat exchanger. If we assume (as my #2) that it's at the stated temps (boiler and rads), the ΔT to transfer 200,000 BTUh is lower, so in operation the boiler flow/return are lower than design 180/160°F (but still outputting ~ 200,000 BTUh).

Cheers........Codey

Greetings.

Reading your statements I wonder at why you have a heat exchanger and what value it gives. All of the boilers that I have worked with (205 in one development) went directly from the boiler to the radiators.

Sooo, please explain what the heat exchanger does. Diagram (a picture is worth a 1000 words).

In process of doing ground temp and multifuel junk oil floor heating and would like to learn about anything that might make it better.

Thanks Oly

That's a good point, but what is baseboard heating? It's not a term used in UK. If it uses oil (or some other fluid) as the circulating medium that might explain why a heat exchanger is needed. Why it should I can't think. I agree with you it would be simpler and probably more efficient to go straight from boiler to rads.

Cheers.......Codey

The radiators need to be pressurized to reach the second floor. The boiler is at atmospheric pressure.

Greetings.

The boilers that I am used to reach to 3 stories with 40 pounds per square inch rating on the T and P Valve (temperature and pressure relief). They are charged by the water pressure in the potable water system through a backflow assembly to the desired pressure.

Water looses ~1/2 psi per vertical foot in heighth. 10 vertical feet looses 5 pounds. To reach the second floor in a two story building which was 20 foot from the basement boiler to the radiators on the second floor and have pressure the boiler was charged to about 20 psi.This system (with a T and P rating of 30 psi) is checked every 6 months to bleed air in the system and adjust the pressure back to the desired pressure for the system. The air has to be bled from the radiators to keep the radiators full of water and working maximum. A cold radiator has air in it.

Two Aquastat controllers and a circulating pump make this system work very well with the boiler and use only water.

Ah, your numbers are so evenly perfect. It does sound like homework.

Be careful if it is; some members will raise holy (%@#) with you if that's the case.

This has nothing to do with homework. Actually I am trying to fix someone else's screw up. I installed a wood/coal boiler in this house some 20 years ago. It has worked fine up until an "outside wood stove dealer" installed this contraption and unhooked the old boiler.

Hi: Al401. If you would like to send scanned drawings and specifications of your current installation, directly to me I would be please to that a look and send you my comments. I would also like to have system drawings and the capacity of the boiler that you removed to install the new wood boiler.

The installation that you describe is similar to a project that I was involved with in hills of Tennessee. This project contained a wood fire boiler with several heat-exchangers that heated the home , outdoor swimming pool and a hot tube.

As Alway: Howard.