Trane XR15 Condenser Size vs air handler sizr

**Bjwc** · 04-04-2013, 04:03 PM

We have narrowed down our heat pump decision to a Trane XR15. The Manual J load calculation recommends a 3 1/2 ton size. One company recommends a 3 1/2 ton Condenser and 4 ton air handler to gain more efficiency in distributing air. In addition they recommended changing to a 10 KW heat strip. Just as a note, we live in Tampa, Florida where it is extremely humid, and we are interested in removing as much humidity as possible.

The second company recommended the 3 1/2 ton condenser with same size air handler and a 5 KW heat strip.

My question: What are the pros and cons of a larger air handler than condenser? Also, what are the issues with increasing to a 10 KW heat strip?

Thanks very much!

**RyanHughes** · 04-04-2013, 04:22 PM

Model numbers of air handlers?

Not uncommon to see a larger air handler quoted. Airflow can and should be set appropriately for the ODU size. The 4 ton will have a bigger coil (greater efficiency) and larger HP blower motor.

Have you discussed thermostat options to control blower speed for further dehumidifcation in cooling mode? Honeywell's VisionPRO IAQ is a good option. You'll want the TAM7 (variable speed) air handler in your location. Your installer can configure the IAQ to tell the TAM7 to reduce blower speed to 80% when ID RH% gets too high. This lowers the ID coil temperature and removes more moisture. The Hyperion air handlers with EEV's perform quite well in this situation. Of course proper equipment sizing is essential, but you said these contractors did load calcs.

As for the heat strip size, depends upon your load requirement (what was your heating load?) as well as your electrical capacity.

**Bjwc** · 04-04-2013, 05:06 PM

RyanHughes,

Thanks for the quick response.

Air handler model numbers are: TAM7A0C42H31, which I understand is 3 1/2 ton and
TAM7A0C48H31S (4 ton).

Thermostat quoted: TCONT803AS32DA. Sorry, but I am a novice to heat pump info, and not sure I understand all your input on the Honeywell thermostat.

Heating strip: I am not sure if this is info required for heating load - from calculation report, 89124 total heating Btu's, CFM heating 1400. Electrical changes are required to change to 10 KW strip strip.

Thanks again for your input with the above options as quoted.

**RyanHughes** · 04-04-2013, 06:10 PM

The TCONT803 is a fine alternative to the Honeywell I mentioned, and similar in many ways. The IAQ does have the ability to do "dehumidify on demand" when set up properly, meaning it can signal the VS air handler to adjust its blower speed when humidity gets too high. The 803 can only overcool by 1-3 deg (field selectable) to control humidity. But, when Comfort-R is enabled (has your dealer explained this to you? you can search this function; most all brands have some form of ramping profiles for greater comfort), I think the 803 will work just fine for you.

For the 3.5 ton XR15, the 3-5 ton VS TAM7 models are all approved matches. As far as the 3.5 ton vs. 4 ton air handler, there really isn't a huge difference in performance between the two. The 042 is physically smaller (a bit shorter), so that may have factored into one dealer's decision to select one over the other. You may already have them, but here are the numbers:

4TWR5042G1/TAM7A0C42 - 12.5 EER, 15.5 SEER, 8.5 HSPF (42.5k btuh cooling, 39k btuh heating)
4TWR5042G1/TAM7A0C48 - 12.5 EER, 15.25 SEER, 9 HSPF (41.5k btuh cooling, 40k btuh heating)

For those who say the 4 ton coil won't dehumidify as well as the smaller coil in the 3.5 ton air handler, there is a very minimal difference in SHR (less than .02 difference) between both combinations. With Comfort-R enabled and the option to use dehumidify on demand, you won't have humidity issues with either combination as long as 3.5 tons is the right size. Your heating load sounds way off (high). What is your average low temperature? A ~90k heating load would be more typical of a 3000++ sqft house in the Northeast, and even then it point to a need of better insulation and home sealing. I think something's amiss there, which subsequently raises questions about your cooling load. And a 10 kW heater package would nowhere near cover your heat loss of ~90k if that is at all accurate.

Since your equipment options are so similar, the better question becomes which contractor do you have the most confidence in to do the best work? In the end, that's what matters most. It starts with doing a load calc properly.

**BaldLoonie** · 04-04-2013, 06:39 PM

A house in Tampa that can cool on 3.5 tons doesn't need 90K heating!

I agree with Ryan, I'd go for the VP IAQ and make sure the dehumidify on demand is hooked up. I prefer that to the ramp profile so it dehumidifies when needed, not just the first 8.5 minutes. If the dealer doesn't know about this feature and the IAQ, forget him.

http://bayareacool.com/ see if they service your area