Can one of you HVAC know-it-alls help me understand the differences between a reheat coil and a heat strip in an A/C system? I know some of the basics, and that the strip sucks energy like crazy. Don’t have a handle on all the factors for making a decision, including any effect on the SEER rating. Situation is a building in FL that has some cooling load, but more dehumidification. Small, budget-conscious house, so not able to justify standalone dehumidifier.
Thanks…
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am just learning AC compared to my RFH knowledge. sorry I can't help. very little AC out here. But it is coming in. I am doing 2 systems this week.
I assume you have a very small heat load, since you are talking reheat instead of primary electric heat and ac..
We use reheat in commercial because the primary load on most commercial building is cooling. Reheaters take two forms, either a duct heater or unit heater in the AHU room. The duct heater is just to boost the air temp in the demand zone, and the unit heaters are supplementals for the whole area supplied by a particular air handler unit. Generally the unit heaters are on the return air side of the system.
Primary resistance electric heat (emergency heat) in a heat pump configuration is in the air handler unit between the return air side and the supply air side. I don't believe electric heat is even used in the SEER rating for heat pumps or ac systems. I have to call one of my systen design guys today, so I'll ask him.
Let you know what he says around 4:oo am tomorrow morning.
Duh, you said small cooling load. Size the unit to the load and the dehumidification should take care of itself. Many contractors will oversize a unit to avoid the "it runs constantly" complaint. Then what happens is the system short cycles and doesn't stay on long enough to dehumidify.You end up with cool clamy air, and the complaint is the system is not cooling properly.
Dave
Edited 6/4/2003 11:59:55 AM ET by DAVERICHESON
It's a smallish FL dome. Cooling load is smaller than the dehumidification need. Some winter heating but not much. If we ran the a/c (2 ton or less w/ 2.5 ton A/H for about 2000 sf) enough to dehumidify to desired level, the house would be too cool because of the way it maintains temp.
If we had a reheat elec strip, from what I've been told, the cost to run the strip would be more than compressor unit. The reheat coil costs more upfront and is a bit harder install, but runs cheaper. I thought the coil was on the supply side rather than the return. Don't know if all of this is correct, but it's what I was told.
Edit: Just saw your edit, Dave, and want to re-emphasize that even though it's FL, these structures have loads that are 1/2 to 1/3 of traditional. Sufficient dehumidification would result in over-chilling the place. At my house, the standalone dehumidification unit runs far more than the A/C. You're right about oversizing--it's a big problem. But it's even moreso on these be/c the loads are smaller than most people are inclined to believe till they see it.
Edited 6/4/2003 1:10:44 PM ET by Cloud Hidden
I missed my Guru yesterday. He is semi retired and took the day off. I'll try agian today.
I think what you are calling reheat is what I would call primary heat in a residential unit. As I mentioned, reheat in the commercial field is zone or area specific.
You are correct in that strip heating in residential units are on the supply side. Ussually located just below or above the evaporator coil. I'll ask the Guru about how it would impact the SEER rating.
Talked to the Guru this morning. His suggestion is to use the correct sized ac unit with a variable speed air handler and a thermostat with an intergral humidistat. When the load calls for cooling, the unit runs at the higher speed. When the cooling call is satisfied, but the himidity is still to high, the t-stat calls for the unit to run at the lower speed and compressor level. This type system would probably be a two stage compressor system.
Guru also said that reheat or electric strip heating elements in a system are not used in the SEER calculations at this time. Expect that to change in the future.
Hope this helps.
Dave
Thank you for following up. I will discuss it with the contractor.
good post