AC help

Tinman

I'm looking for a high efficiency solution to replace a number of small commercial air handlers and condensing units.

Here's what I'm looking for - 6 ton thru 10 ton split systems with a high SEER, ideally 16.
Here's what I'm finding - these systems top out in the 11-12 range.
Is there something out there that fits this description?

Another idea - I've twinned furnaces before and twinned evaporator coils tied into a single larger condensing unit, but that leaves me with the same scenario as above. Has anyone twinned two air handlers, two evaporator coils, 2 condensing units? Is it even possible? With the manufacturer's blessing? This way I can get whatever SEER rating I wanted.

ratio

I've twinned furnaces with one big condenser (both single & two circuit) and two li'l condensers. Works fine. I prefer to stage them in if possible. A 9000 series Honeywell with a RedLINK EIM will let you do four stages of heat or cooling…

One gotcha is that the furnaces frequently need to be on the same leg of the panel so the xfrmrs don't fight; & I think it might have something to do with the flame sense as well. IDK about air handlers.

EBEBRATT-Ed

I can't think of any reason why AHU'S could not be twinned.

I know Carrier used to twin furnaces and had twinning kits

cashheatandactech1

yep , you will just have to get a little advice from your local distributor, and purchase some units that can be twinned and a twining "kit" pretty much cables and such. that is the easiest and least confusing, because the circuit boards are already to be twinned just have to initialize it.

JUGHNE

I work on a building that has 2 sets of twins, each NG FAF runs 5 tons AC. One large common return duct for these 4 and one other loner.
Each set now has 2 stage T-stats. The control boards must match and wiring was simple once the knucklehead install was corrected.

I was told that variable speed blower motors might not work with a pair of twins sharing RA ductwork....apparently they arm wrestle with each other with a little static change.
Any comment on that by the Wallies?
The variable blower usually added 1 SEER IIRC.

ratio

Many modern furnaces have a 'twinning' terminal, that's about all that's required for them.

I've installed 3rd party twinning kits before too, they were nothing more than a rack of relays to stage in the units. Honestly, a handful of RIBs (I'd use a handful of DIN rail mounted Idecs for prettification) will be all you need. Make sure the fans are tapped to the same speed is the only real concern.

SuperJ

LG makes a nice kit to retrofit VRF condensers to an existing AHU DX coil. You can control off discharge or space temp. Available in a range of tonnages up to 48ton.

https://www.lg.com/global/business/air-solution/vrf/air-handling-unit

ChrisJ

@njtommy

Tinman

@JUGHNE I've heard only PSC motors can be used too.
I've also read that if you twin two 5 ton furnaces, you're not going to get 4000 cfm. More like 3400 cfm.

JUGHNE

I wonder if that is because of having a common return duct?
Pulling a negative on a negative maybe?

Ironman

Steve, don't confuse SEER (seasonal energy efficiency ratio) with EER (energy efficiency ratio). EER is what the unit does at 95* outdoor, 80* indoor db, 67* wb.

SEER is a formula that allows for varying outdoor temps to be calculated in because the unit becomes more efficient as the outdoor ambient becomes lower. Residential equipment (5 tons or less) has both a SEER and a EER; commercial only has the EER.

If you'll check the EER on residential, most of it is in the 11 EER range. So, you're not really gaining anything by putting in two 16 SEER residential units that have an 11 EER, except staging capability.

SuperTech

I've seen twinned First Co. Hydro air units used in a commercial setting. Just a mess of relays on the older ones. The newer First Co units with the CB201V control board are easily twinned with RIB relays. All the twinned units are PSC in that building.

njtommy

You would be better off going to VRV system with 1- 2 condenser tied together and a few branch boxes. To handle all the different areas.

Tinman

That’s exactly what I recommended 😎

ratio

If you're going to go VRF, please get the heat recovery model, don't go with a straight heat pump!