Water to Air Heat Exchanger in Furnace problems

[fpc310]

Thanks Neighbor... glad to be here.

My lines are buried nearly 4 feet deep. I went a little nuts with the ditch witch when I trenched the line. The ground is frozen solid and snow never melts!

My water lines do not circulate 24/7, only when one of the furnace units are calling for heat. I see some argument on this forum on whether 24/7 circulation is a good or bad idea. Thermostat controlled pump relays are the standard Hardy setup.

I am not really complaining about the wood usage. I think I will change the system to run in series today. I am also going to see if there is air in the system. I am hoping this makes the difference.

 

[Hawken]

I have my cb5036 with a taco pump running 24/7. I have the loop running first to a side pipe attached to my water heater and then to my HX in my furnace.

Running the pump 24/7 keeps me supplied with 50 gal of 170 (or so) degree water and warm duct work. My electricity bill was down over $100 the first month mostly because I have the hot water turned off and I am not running two blowers on indoor wood stoves.

I was burning about 1 to 1.5 face cord a week with my old stove and I am burning just under 2 per week now. But now my house is always in the 70's and I can take a half hour shower even after my wife took a shower, my kids took a bath, wife washed a load of clothes. I can't believe how much better something like a wood stove has made my life.

Loading up a wood stove outside is much better than hauling wood in the house, cleaning up the mess from dirt and ash. My kids are much healthier because of the consistency of the house temperature, and no mold from bringing wet wood.

 

[Marklambert61]

Issues

Supply and return pipe size: 3/4 Pex (as recommended by mfr)
Pump type and size: Taco 009
Length of run of plumbing: OWB To House Furnace: 75ft
Length of run of plumbing: House Furnace To Garage: 40ft
Water temps at boiler in and out, at coils input and outlet: I don't have these metrics at this point. I am in need of some inline temp sensors to help me measure this. Any recommendations?

Hardy seams to classify their exchangers by tonnage, but it is in fact a 130K BTU exchanger at 2000cfm w/ 3/4in NPT connections. This one works very well too. The exchanger in the garage is a 120K btu exchanger w/ 1in connections (american royal brand). I have it also hooked up to 3/4 pex using reducers. I know I am not going to get 120K BTU with such small lines, but I was hoping for at least 80K.

Todd

Todd,

1. Here the deal issue by issue...

2. Pump if fine but the rest of your system is capible of about 60K BTU's only

3. Your pex lines are 50% of the size you need for the BTU's your looking for
1 1/2 lines are needed.

4. Plumbing is an issue you need you plumb them in parallel with 3way zone valves so the loop will circulate continuously. But that's only a solution if you put the bigger lines in to feed the system.

Better fix in my opinion is to install a second set of lines from you house to the boiler 1" min then plumb the water heater and bigger unit as a stand alone system. Let the second unit operate independently.

This should be possible with still using your single pump however its going to be close pump could be an issue.


Mark

 

[trialanderror]

since we're on the subject.

if i plumbed 2 exchanges in series, could i effectively pull 120F air from both exchangers with 180F water with 1" pex supply lines from the boiler with a pump doing ~7gal/min?

edit

haha, i got ahead of myself


found this link, i'll post it for everyone else
http://www.heatexchangersonline.com/airtowater.htm

 

[projectsho89]

since we're on the subject.

if i plumbed 2 exchanges in series, could i effectively pull 120F air from both exchangers with 180F water with 1" pex supply lines from the boiler with a pump doing ~7gal/min?

Probably not.

The rate of water flow is the same in both exchangers in the series circuit.

The first exchanger in the flow path will get the 180F water and will give up it's maximum possible heat (based on airflow and surface area), probably 15-35 degrees.

The second exchanger will get the water that is then 15-35 degrees cooler and the airflow will only be able to extract a proportionately lesser amount of heat from the exchanger.

The return water back to the boiler in this example might as low as 110F - 150F making that quite a bit of a shock for it to try to reheat, especially if there isn't enough mass of water in the system.

Chances are, you'd likely see 120-125F air temps off the first exchanger and only 105-110F off the second (off the cuff guestimates).

Steve

 

[david78]

Back to getting air out of the HX: if the OWB is the high point of the system, wouldn't any air just migrate to the water tank at the boiler?

 

[mtfallsmikey]

Yes and no...air can get stuck anywhere....as far as the 2 coils in series, I would like to see the specs, but p-shoe89 is right.