Same unit, but I lack knowledge
I have the exact same unit as MPatrick (which is how I found this thread)...hoping someone can help me out even though this thread is a year old now.
We live in NW Florida about a mile from the gulf. The internal square footage is considered to be around 2150 (+- 50 s.f.) but our ceilings range from 9 to 12 feet high (probably averages about 10.25'). It is a single story home and while we had a very reputable builder, at the end they do an energy efficiency rating on the home...out of 0 to 100, it was 96 or so, with 100 being worst.
We got the same unit as MPatrick as we wanted to cool the garage for additional usable space, though we took no other measures to make that space energy efficient. One drawback, though, is that we usually do keep the garage door closed (leading to the house) and when doing so, the return air draw is enough to pull one door in line-of-sight closed on occasion.
We have very low energy costs per kWh, which is part of the reason I believe most builders here are so poor on energy efficiency. Our cost is about 7.6 cents per kWh.
We are also VERY liberal with our house cooling and with our pool heating (both due to health necessity). The house temp is typically 71 - 73...occasionally, 74 or 75. The pool is usually kept around 93 degrees. The pool is covered with a scroll compressor heat pump of high efficiency (sorry, but I do not have the rating handy), so while it is still somewhat pricey to heat, I estimate it contributes an average of $110/mo during the 7.5 months/year we operate it.
For one year, we were in a program where we could buy our energy at different prices (based on consumption and time of day)...however, it required having a land line....so when the phone line went, so did that program.
We have gas and electric (the gas is also of poor efficiency....80.5), but the electric accounts for roughly $3000 annually. However, it seems to be worsening year-over-year. We just had a record $410 electric bill at the rate I described (7.6 cents/kWh) in addition to a $45 gas bill. We have had our Rheem (11 seer) since building the house in 1999 and I have never been impressed with it other than its ability to cool the entire house even when temps are in the upper-90s day after day. That is where our temps peak out...we do not break 100.
I am strongly considering any and all measures to increase the efficiency of our house/appliances. The washer, pool scroll compressor heat pump, and refrigerator are the only high efficiency devices in the house. From what I can tell, the A/C and possibly the dryer (though that is occasional in usage) appear to be the largest consumers in studying the meter. While just about everything was running last night, we consumed an entire kWh in 3 minutes 6 seconds! We do have a number of computers which are always on (not the monitors, though), but during periods where the energy guzzlers are not running, the wheel will make a 1/12 kWh rotation in about 13 seconds. That seems to be our low rate that I have witnessed. Still, that would come out to far more than the 140 - 160 kWh/day we are averaging...I'm not sure what changes when we go to bed to slow the rate down farther.
Unfortunately, you can see I know next to nothing in this area save trial and error...I know nothing of the internals other than that the same model Rheem indicates it also has a scroll compressor. That's basically where my [lack of] knowledge ends.
Stop cooling the garage.
You make it sound like it has no return in it, so that means the system is putting your house in to a negitive pressure and pulling in outside air, when you have the door closed to it.
Pools around here aren't heated above 87.
Add insulation to your attic, see about upgrading your windows and door, weather stripping.
Then you might be able to get a higher eff smaller a/c.
For the garage, we do use that as additional living space (though as I mentioned, it has standard insulation or lack thereof). We have parked a car in there only once or twice in 6 years. However, due to homeowner association issues, we cannot convert it to a room per se...the attic above it is commonly shared with the rest of the attic above the house. We installed a fan after H. Ivan repairs to provide some exhaust.
The insulation is, I believe, R-38 (for the thick areas)...but it is the lousy(?) blown fiberglass. I can only speculate how much that costs us and would absolutely consider redoing it if you think it would make a significant difference. I think most other walls are something like R-13 or whatever Florida standards are.
You are correct on the lack of the return air...the AC was upsized to that Rheem with additional output as well as an increase in the SEER from 10 to 11 (which to me seems anemic given the 12 SEER we had when living in MD beforehand).
Can you explain more about the negative air? We typically keep the garage door closed despite the fact that the air flow was designed (capacity and draw) for it to be open due to pest wars in the garage (home sweet home to the roaches and the like).
I know we keep the pool super-heated, but that is because we typically swim at night when it is cooler. I do use a solar blanket/hand reel.
Part of the problem is that we do heat the pool to high temps and cool the house to low temps, but we do not wish to give that up. When evaluated, our A/C system was putting out around the 50 - 60 degree mark, so it is working like it should at least in regard to output. However, I don't know if its poor efficiency and/or the house's poor efficiency are what cause the bills to be excessive. The gas bill is never an issue...I think its all-time record is perhaps $110 - $120. The stove top only, the water heater, the house heat, and the grill are the only devices using gas. All others use electric (not heat pump save the pool).
Would replacing the blown fiberglass make a notable difference? Can it be roughly quantified? We do not have any weatherstripping in place. The windows are double-paned. I recall when the house was being built that there tended to be significant gaps around the framing and the sliding doors. We have quite a bit of glass in the house, though the majority faces (in order) South, then North, then West, then East.
Few garage doors close with a tight seal, so your loosing conditioned air aroung the door(my guess).
When you loose air to the outside, it has to be made up some how, and thats by drawing it in any where else it can, such as gaps around windows, and other doors.
I don't know how you got around code, to have a supply in the garage.
South windows, do you have good heavy drapes, and close them when the suns shining through.
They may have fluffed the insulation when they blew it in, meaning you don't have r38.
You can lay insulation over it, or have more blown in.
Again, around here 87 for the pool, and we swim at night also, so it can't be any warmer up here in PA. That extra 6 degrees can be alot of money in electric.
Some pools up here are only heated to 83.
You may want to have a contractor check to see if its feasable to zone you system, so youor not cooling areas of the house your not using for 8 hours. This can also save alot.
how do you get your home rated for efficiency?
I would do the following
1. swap all your lighting for fluorescent bulbs
2. put that white insulation powder in
3. put those roof turbines (the passive ones)
4. check for duct leaks
5. put the weather stripping to seal air leaks on windows/doors
6. swap out the AC for one of those fancy Carrier infinity systems
7. run your pool pump 4-6 hours only.
My electric bill now so far is averaging 120-130 a month and I have a large saltwater tank with PC lighting/pool with large pump.
my bills used to average 345 bucks a month
in 10 years thats going to be 25,800 dollars.
not a bad investment. [I had #2 though previously I did 1,3,4,5,6,7]
One thing to think about -- is there some way to utilize the cold air being produced from the pool heat pump to cool the air conditioning condensers (stack them and use a huge diversion duct)? Ideally, a common heat exchanger system would be used, but this is complicated. Perhaps find a way to blow the pool HP cool air into the converted garage space.
Also, do you have sun shining on the pool HP and shade on the house AC's?
Accoding to these numbers you have a total capacity of 35,947 btuhs. That model with a matched piston coil has a capcity rating of about 40k. You are lacking 4,000 somewhere.
Originally posted by mpatrick
Expert opinions please:
RAT DB 71
RAT WB 65
SAT DB 60
SAT WB 59
Evap TD 11
Your sensible BTUS however is only showing a 18,829 meaning the latent load is very high (almost 50% of the total system btuhs. Look at your return numbers...
65WB and 71DB? thats 73.11% rh!!!!!
I would expect with high airflow and such high humidity to see the 11 degree drop. The fact you are using a mismatched coil may have something to do with the cpacity loss. Hopefully with the new coil, dropping the airflow to 1400 and finding out how a unit doing that much latent work can not be reducing that humidity.
I just realized you guesed at the CFM by looking at the blower door chart without actually reading the true static.
"Thanks Doc for looking that up anyway"
"NP dude, I wasnt doing anything anyway"
Your airflow may be higher or lower in which case all my response is bogus.