Dehumidity on Demand
I have just installed a new unit.
1. Trane XL16i 4 ton 2 speed. 4TWX6048G100A
2. Trane Hyperion TAM7A0C60H51SB
3. 10kw heat strip
4. Honeywell Prestige IAQ 2.0 thermostat
5. Honeywell EIM
6. Honeywell HZ432
7. (2) Honeywell TH6320R1004 Wireless FocusPro thermostat
8. Honeywell Redlink Gateway
House is in Central Florida and about 2600 sqf.
Currently have the system up and running(by local AC company which did a good install but not quit up to speed on the Honeywell products). My questions are:
1. From research I should not use Comfort-R(Enhanced Mode) but what about humidity on demand? I have been told that activating this function of the Honeywell IAQ will reduce the life of the HP. My installer told me that using the AH at a reduced rate(80%) and the HP at 2nd stage(dehumidification mode) will reduce the life of the HP(my main question).
2. I have 3 zones. A large family/living/dining(60% of total area), bedrooms(3 kids b/r on 2nd zone(30% of total area), and bonus room(10% of total area, but the largest heat load(outside walls on 4 sides and top and bottom)). Today I switched the HX432 from timed to zoned(I do not have dehumidification or Comfort-R enabled). Should I use TSTAT or %Zone for control of 2nd stage?
3. My ducting is the limiting factor(10 years old). Dip Switch S1-1 and S1-2 is set to on-off(4 ton). Dip Switch S2-1 and S2-2 is set to on-on(400cfm).
What are your ideas to make this system to operate most comfortable and efficient?
What is the temp/%RH typically in the home?
I hope the bonus room gets more than 10% of the air flow or it could kill your compressor .by going to % of zones when the bedrooms and bonus room call foor cool the unit will go to high speed will the duct work handle 4 tons of air or does it have a bypass damper . I would turn on comfort r
If the system was sized properly you should not need DOD. I would set comfort R and run it as is.
Originally Posted by Hobie5x5
TB. Prior to the changeover to the new 2 stage system(the old one was a Trane single stage 4Ton unit), the main area need to be around 76-77 to be comfortable. Now I can keep it at 80F(RH around 45-50% on the Prestige IAQ 2.0 and it feels good). Currently neither Comfort-R or Dehumidity on Demand with the HW Prestige IAQ 2.0 is enable. I am thinking of having the installer leave the Comfort-R off(because it is not needed every cycle) and enabling the DOD using the Prestige thermostat unit(45%humid) using the BK terminal. Currently the humidity is running around 50-55% since the installer changed from timed to %zoned on the HZ432. My installer is reluctant to enable DOD because he says that running the AH at 80% and the HP at 2nd stage will shorten the life of the HP. IS HE Correct??? Since I am running a zoned system, on the HZ432 should I run TIMED,TSTAT or %ZONED. Now have %Zoned and it seems to make the most sense.
catmanacman...I have remove the manual bypass and installed an Electronic Bypass Valve. But the flow on all zones seems to be much less than before the system changeover(maybe this will be better???)
Second Opinion...I did think about Comfort_R but the system is generally running in the 50-55%RH range. Today it rained and the humidity crept up to 55%. If I use COmfort-R every cycle will be Enhanced mode even if I do not need it. But of I use DOD, only when the RH is above 50% will I use 80%AH and 2nd stage HP. Am I thinking of this correctly? My installers did a great install but fall a little short on the wiring and programming. They are recommending to not use the advanced features of the 2 stage TAM7/XL16i and Honeywell Prestige IAQ 2.0 system.
If I use DOD and the AH runs at 80% and the HP runs at 2nd stage, will I shorten the life of the HP?
I have spoken with my installer and will do what I want but any recommendations or guidance for both of us would be greatly appreciated.
BTW. Today the outside temp was mid 90's and I had 2nd stage on and off for 3-4 hours. The house probably should have been a 5 ton unit but the ducting will not support it.
Basic a/c setup should have the air flow set through the cooling coil temperature for <50%RH in normal use. Typically coil temps that are 25-30^F below the desire room temp provides <50%RH. Sounds like yours is setup correctly. As the cooling loads seasonaly decline, <50%RH gets more difficult. Over-cooling helps a little. Two speed or VS compressors as reduce the short cooling cycles which reduce the moisture the a/c removes.
When the cooling cycle is occasional, adequate moisture removal by the a/c is impossible.
Moisture in the home comes from the occupants and fresh air infiltration/ventilation. A healthy home needs a fresh air change in 4-5 hours as minimum to purge indoor pollutants and renew oxygen. With a +65^F outdoor dew point and a couple occupants, 2 lbs. of moisture per hour needs to dehumidified from the home to maintain <50%RH. Without a significant cooling load, complicated a/cs are unable to maintain <50%RH. A whole house dehumidifier is able to maintain <50%RH without any cooling load. Also controlled fresh air filteration/ventilation is an option.
During the cooler times I will use a portable dehumidifier. But now I am thinking of having DOD wired up. Does DOD(AH at 80% and HP at 100%) damage or reduce the life of the heat pump?
I understand your question and your conncern, I am pretty sure Trane has engineered the hp to take 100% compressor with only 80% fan. This is the engineering behind dod, to dehum on low load days without much cooling droop. I would either run the dod or get a whole house dehum as teddy says. Me personaly I like bringing fresh air into the return and running dod.
You can try over-cooling manually by reducing the set point 3-4^F then the set point.
Originally Posted by Hobie5x5
Keep in mind that over-cooling will lower the coil temp automaticly.
Using your dehu is a better deal energy wise. Over-cooling uses a fair amount of energy with marginal moisture removal.
Residiential dehus remove 2 lbs. per KW.
A/c removes 1-2 lbs. per KW
High eff. whole house dehus like the Ultra-Aire remove 4-8 lbs. of moisture per Kw.
Keep us posted.
I like the idea of the Ultra-Aire but it is rather pricey. I think I will try the DOD first and see how it does. The only concern that I have is that my AC installer said using DOD will reduce the life of the HP. Is he correct or misinformed?
Thanks for all your help.
Please refer to my last post where I stated I am pretty sure Trane engineered it to be ok. Thats the best you are gonna get from anyone on here. Better yet, I would call the factory with that question they would know ;)
Originally Posted by Hobie5x5
Thanks. I do appreciate your input. I assumed the system would be OK. Just thought I would ask.
Sooo many factors go into equipment life. Using DoD and running at 80% airflow part of the time I would consider a very, very minor factor.