forced air furnace coil + hybrid furnace control questions

[pjf]

Question 1
Central Boiler and Alternative Heat Supplies have a good selection of forced air, water-to-air coils:

(broken link removed)

(broken link removed to http://www.altheatsupply.com/index.php/shop-by-needs/outdoor-wood-furnace-parts/water-to-air-exchangers/120-000-btu-water-to-air-heat-exchanger-1025.html)

Anyone else I should look at? (Preferably a Canadian company..)

Question 2
I've read it's good practice to remove these things in the summer... but how bad do these coils affect the efficiency of the furnace when running in NG/LP?

Question 3 (for the controls freaks)
How critical is it that LP and the 'zone' are never on at the same time? I'm wondering if I need a discrete switch between LP and the Boiler?

I was thinking of using a water temperature switch set at (lets just say) 130deg*

If (Boiler = ON) and (Temp < 130) and (Thermostat Contact = Closed)
Use LP, Zone On**
If (Boiler = ON) and (Temp > 130) and (Thermostat Contact = Closed)
Use Boiler, Zone On (obviously)
If (Boiler = OFF) and (Temp < 130) and (Thermostat Contact = Closed)
Use LP, Zone Off
If (Boiler = OFF) and (Temp > 130) and (Thermostat Contact = Closed)
Use LP, Zone Off

*with adjustable deadband

**My thinking was that if the boiler is ramping up, is it a big deal to have some circulation to help get the water up to temp?

 

[Tennman]

Question 2:
People recommend removing the WTA HX from ductwork every year? Really? Then it would also be a good idea to remove the AC condenser coil before winter. I think I paid about 8 labor hours to have two HVAC technicians install my WTA HX. At least in our case I'd never dream of installing and removing each season. Maybe I didn't understand the question..... BTW, our HX is in the LP furnace ductwork and when we go LP for heat I can notice the air warms slightly as the WTA HX is brought up to temp by our LP furnace. Our boiler puts out much warmer air than the LP when it's providing +140-150F water. Love it when we're sending above 160F water. Fan doesn't run nearly as long.

Question 3:
Before adding storage last season the boiler demand pump would come on when the boiler hit pump "on" temp set in the controller. So there were rare occasions when we had the LP on to warm the house in the morning while the boiler was getting up a full head of steam. During those brief and rare occasions I was willing to waste some LP to knock the morning chill off the house. Now with storage the boiler demand pump only runs when the boiler tstat commands the furnace blower on. I think using LP to help get the boiler up to temp is a poor use of expensive LP. And BTW, with storage we rarely had mornings when we needed to knock the chill off. Even with stored water temp down in the 120's F and the fan running continuously, the house never cooled off like it would before storage. Storage is a game changer.

I hope I answered your #3. "Zone" is typically used to discuss radiant systems. In our case with forced air we don't, or at least we don't, have "zones". One duct system so that's it. If I understand your question, I try to avoid using LP to help the wood boiler since it's using the far more expensive fuel to supplement the cheaper fuel.

Also, I think I used All Heat Supply for our WTA HX and they nailed it for the specs and duct size we gave them. I called and discussed over the phone, the tech did some math... seems like it was semi-custom for our duct size. But it performs exactly per our requirements based on the boiler design output and the furnace fan's CFM.

I hope that helps. I kinda think I answered what you are asking. Gotta to make money.

 

[rkusek]

no need to remove the hx. I put shut off valves and turn them in summer so boiler water does circulate thru the HX. I can't imagine much energy is wasted leaving it in if the water can't circulate.

 

[rkusek]

For the controls we would need more info on your boiler. Like Tennman said you don't want to heat your boiler using the heat transfer from the LP furnace. A few years back I ran my circulator continuously on a cold weekend when we were out of town so I didn't have to worry about the boiler freezing. Well it worked, boiler and all the piping down in my shed were at 70 degrees just like the house. If you are planning on an OWB and LP furnace the controls should be simpler than gasser with storage and heat pump like mine. A HP can have multiple stages of compressors, defrost mode, and Aux heat. I use a separate tstat set 2 degrees warmer to control my wood heat. The tsat uses the resistance heat setting and I think it comes on before the display even shows 1 degree less. Bottom line home is always exactly 70 degrees when boiler water is at least warm. When boiler water cools below 100, the home will have to cool down to 68 before the HP kicks on. Fortunately HPs work the same way and maintain constant setting, mainly because they only put out lukewarm heat and have much more run time than a natural gas/LP furnace would have. My family and I actually prefer the constant temp vs. the hot-cold hot-cold we had in our last home with a hi-efficiency gas furnace.

 

[pjf]

Appreciate all of the replies. I think I'm going to keep things simple for the first winter... My background with controls can be a curse. :D I have a feeling I'll be migrating towards a storage solution over the long term, it seems to solve the biggest issues when looking at the big picture.

And yes, not to mention any names, but there are at least two regular users on here who claim to take out their WTA HX every summer. A before/after CFM reading would quickly show if it was worth the effort.

Two Copper Unions, some thoughtful plumbing, and some fabrication skills for the mounting brackets... it would be like pulling a radiator out of a car.

 

[Armaton]

Outdoor Furnace Supply (OFS) advertised on this site, has many sizes of WTAX's. They can email you the specs for them also, ie gpm/water temp needed/ and cfm for what btu output you may want. If you are going to remove the WTAX, make sure you put in a way to purge the air out if you have a closed system! If open, no need.