I know its a hydronics site, but FA question

Mitch_4

Looking if anyone knows a control that will operate 2 forced air units simultaneously. Buth units feeding common ducting.

I can easily work it out with relay logic, and sailswitches (for safety) but would prefer an integrated control (like tekmar) to avoid the "spaghetti factor"

Anyone ever heard of such a beast?

Thanks.

Mitch

Tom Blackwell

Most manufactures offer a "Twinning Kit", which includes the control interface, etc. It's been a long time since I dealt with one though.

Mitch_4

Gas ones I can get, but this is for oil.

There is no kit from the manufacturrer, and I know of no oil furnace that does.

Mitch

Firedragon_4

I've used a

hydro-air relay to twin them, but I really think using a two-stage thermostat to control each burner (on demand) is a good way to go too!

Using a DPDT relay aka R8845U or similar has been done and it works.

I just let the blowers do their thing and recently helped lay out a retrofit that used furnaces that had electronic boards and ECM motors, very nice.

That ECM motor with a temperature sensing controller is, IMO, going to create some nightmares for us who love hydronic heating and it's got GE pushing it, so........look out!

http://www.geindustrial.com/cwc/comfortcenter/gecchome.htm

I just finished writing a new training module on these things and .................... well, like I said look out!

www.firedragonent.com

Matt Clina

Suggestion

In addition to the control aspect, you might want to install backdraft dampers between the furnace discharges and the common duct. This will help prevent backflow if only one furnace is running (to keep from blowing the dust back out of your filters and return ducts).

clammy

On the subject

While on that twinning subject i feel that it's always better to set the units on a heavy gauge duct of a least 10 to 12 inches deep espically if your unit have a 5 ton blower one cut out on each side is not enough and in the middle is not enough i have seen to many units twinned improperly usually leads to return whistling and premature burn out of the motor had a variable speed motor go recently peace clammy

Mitch_4

That is what I am using the sail switches for

One of the concerns is that if there is a limit activation in one unit, it shut both down, or activaltes mechanical louvers to isolate that unit from the duct system, and prevent air from circing through the limited out unit. (path of least resistance)

Might be easier to design and market one.

Thanks all

Mitch_4

I will be

running a "pair of pants" return, with a a 2 foot dividing panel in the main and an adjusment plate to balance the flow.

I agree, that too many twinnings are a problem.

Me_8

Not sure if its still available johnson controls had a nice twinning kit, it was made for gas but would work with any oil furnace that is "A/C ready" it used current sensing relays for the blowers. could use a 2 stage stat and it would switch the lead and lag furnace and air all on its own.

bill_51

honeywell makes a twinning control. i've used several of them and there was only one bug. if used in cunjunction with fan control boards on a furnace, the control sometimes may pick up the "bump" as the board turns on the 2nd stage and for that split second disengages the fan on the 2nd stage unit. different control boards for different furnaces. this furnace was a york. problem can easily be overcome with a simple relay

Mitch_4

Do you

have the honeywell / tradeline part number?

Thanks.

Mitch