There was a small amount of controversay back in 2003 when I was picking your most talented brains for information to help me design my new house, and I had said I would give a followup after the system had been in operation for a while.
House: 4000sqft (2800sqft in a two story section, and two 1-story sections adding up the other 1200sqft), slab foundation, NW Arkansas (south of Branson, MO)
System installed: 3.5T 14SEER (13 SEER plus TXV) Tappan heat pump with VS air handler. Arzel 4-zone system. Duct work is oversized, so that each zone can take the airflow.
System is working pretty well, except the airflow is really a bit much for the smallest zone (noisy flow, and we had a Bernoulli effect issue in the family room bathroom, definitely not a room you want the supply system sucking rather than blowing). But overall pretty good.
Winter: 3.5T HP handles temperatures down to about 25F without auxilary. Even down to 7F, the auxilary heat doesn't fire all that much.
Summer: 3.5T is too much capacity for a 92F outside temperature, on this zoned and well insulated house. The system does not run long enough to do a really good job dehumidifying. My father-in-law across the street has a 10SEER Tappan, and it does a great job dehumidifying.
I have an all electric house, with two 50gal 95% electric water heaters. The electric bills, for this 4000sqft all-electric house, along with my home office, run $200/month on bill averaging.
The home office: I have considerable amount of energy consuming equipment, so I have an 11SEER supplemental AC unit handling the heat load of this room. The low speed VS fan sweeps the rest of the house nicely, but it's not sufficient flow to sweep the heat production in my office.
I used Don's wonderful HVAC-Calc program to generate my stab at the calculations for the hosue, then used that data to shop for an HVAC professional to do the final design and installation. Was amazing the people who disputed my calculations and insisted the house needed at least 5T. One guy insisted the house needed 5T downstairs and 2.5T upstairs. If I had to do it all over again, I would have pushed harder for the system to be downsized to a 3T, or I would have tried to hold off for the few additional months necessary to get a Copeland UltraTech scroll.
Thanks again for all your wonderful advice and inspiration!
Thanks for the feed back!
A few questions...
Is the small (noisey) zone calling for high stage by itself?
Do you have a Bypass duct on the system?
Is the HP two stage?
Does the V spd air handler run at a lower speed for single zone cooling calls? This would greatly help in dehumidifing.
Thanks again for the detailed feedback...very valuable info!
"Calling for high stage by itself"...I'm not sure what you mean by that. The small zone is able to call for service exclusive of the other zones. When another zone is active, there's no velocity issue with the small zone. It's only when it's the only one calling that we encountered the issues. But a diverter resolved the bathroom reverse flow issue. It's still a bit noisy, but not objectionable.
No, there is no bypass duct. The contractor sized the ductwork for each zone to be able to handle the whole flow. With only 5 ducts on the smallest zone, that is of course the most problematic when it's the only zone calling, but it's livable.
The HP is single stage. I had it installed just a few months before the Copeland Ultra Tech was common. At the time of installation, only Lennox was actually selling units with the new dual stage Copeland, and I'm pretty partial to Copeland over Bristol or Tecumseh compressors. Go figure.
No, the VS air handler does not have any knowledge of how many zones are calling; the Arzel zoning controller handles all that info. Given that, the Tappan VS AH does have a DEHUM input that is currently jumpered shut, and I've been contemplating having a humidistat installed. Bald Loonie mentioned a $25 unit that was very servicable, but I never could find the actual make/model on that unit. But I completely agree, it would be quite nice to be able to control the top speed of the variable speed motor according to the total zone demand currently active, both from a dehumidification and from a noise (on the small zone) perspective. Guess I could cobble something up with one of my humidity sensor ICs and a relay, but I typically stay clear of things that might be argued to void my warranty.
BTW, I'm in the process of building a remote pressure sensor using those wonderful Freescale pressure sensors, so it can send my computer a message when the pressure drop across the filters (dual 16x25x4 media filters) indicates it's time to replace the filters. Yeah, I could do it much more effectively with a simple $60 manometer, but where's the fun in that?
Some day, when I get around to it, I'll build a zone controller controller and replace my thermostats with intelligent remotes. Then, I can insert enough delay into the zone calls to get them to line up properly for longer run time, (and longer off time between calls) which will help with efficiency and dehumidification even more. While I WON'T do this, because of the wonderful warranty issues, the ultimate solution would be to directly control the settings on the VS motor, like you hinted at above, and set the top speed of the motor to match the instantaneous demand, for optimum airflow at all times...
Oh, BTW, since you work for Arzel...a bit more information about my experience with the Arzel Zoning system. I've been really, really pleased with the Arzel system. It has worked flawlessly so far, and it's very quiet. I have one damper that just in the last couple of months has started to squeak occasionally, but it's not a big deal.
[Edited by gstovall on 05-14-2005 at 11:44 AM]
Have the humidistat installed, it will make a world of difference.
Also, what cfm is your blower set for in cooling, you might be set for 400 per ton, when 350 might work much better for you.
gstoval can you forward to me any equipment information, wiring diagrams for the air handler preferably. There are some simple things we can do that should eliminate excessive air delivery to that small zone. I need to know a little bit more about your air handler wiring options.
We should also be able to utilize the Dehumidification feature if you need that.
If you can get me the Tappan Mdl# I should be able to source out the info I need.
beenthere, when I investigated the humidification issue last summer (started looking, because while it cooled really well, there was barely any condensate coming from the condensate drain, and the humidity was staying in the high 50s), I discovered that the cfm was set to 1450, which was of course way too high for a 3.5T unit. I set it to 1250, which was the proper number for 350cfm/T at 3.5T, but I didn't see any improvement in dehumidification. In fact, I dropped it all the way to 960, just to see what would happen. All that happened was insufficient airflow from the vents, with no improvement in dehumidification. This really, really puzzled me, because I know from reading this most excellent board that reducing the air flow should result in a colder coil and better dehumification.
jramunni, the AH is a B3VM036K-B. Actually, the case is the PSC motor version of this, but the contractor replaced the PSC motor with the approved Emerson ECM VS motor and control board. Said something about getting the same configuration for less money...
When the machine with the scanner comes back on-line (hard disk failure; I'm waiting on a replacement. I need to start stocking spares), I'll be happy to scan the wiring diagram and email it to you.
How does it heat.
Did they double check the charge, or just weigh it in, and say good enough.
Did they check the delta across the coil.
That's the strange thing. It both heats and cools well. In the winter, the auxiliary heat hardly ever kicks in, and then only below about 22F or so, and only for brief periods.
I've checked the deltaT across the coil and it's running about 15F, which is right in the good range.
Yeah, I know; something doesn't make sense. The deltaT should have increased when I dropped the airflow. The only thing I could think of at the time was that the TXV was adjusting the coolant flow. Don't know if that makes sense, though.
Around here, 15 degree delta won't dehumidify below 60% rh.
It might be slightly under charged, and the txv is wide open to get you that 15.
Also, if they had to install the txv, they might have over heated it, or damaged the power head, something is not right.
Could be the bubl isn't mounted right.
They need to check the sub cool, and super heat.
I had the company out, and they checked it out. Determined it was about 1.5 pounds low on R22 and charged. I watched while he charged, and he was charging by superheat rather than subcool measurements. I'm sure I was probably aggravating him a bit, but I was kind of specific that I was interested in the subcool measurements, and he said that when he was all done, he took a subcool measurement and it was 12F.
Haven't noticed any appreciably difference yet, but we really haven't had any consistently hot weather yet, so the AC hardly ever runs so far. We've had a few 92F days, but with the insulation, the system doesn't turn on until mid afternoon, then it cools off quickly at night, so it really has to be an extended period of hot weather to get the system to run all that much...
I'm accustomed to the water gushing out of the condensate drain on 10 SEER systems, and my father-in-law's 10 SEER system, installed by the same company, maintains a 40% RH very easily. Are 14 SEER systems really that much worse at dehumifying? It's just a drip every second or so, but the service man didn't seem concerned about the condensate rate.
Next time it cycles on take another delta on the coil.
If it was 1.5 lbs low, you should see a better split.
What temp are you keeping your stats at.
Keep the master bedroom at 78F and the other 3 zones at 77F. Personally, I prefer it cooler, but my wife freezes even at 78F right now (some kind of protein deficiency).
There are 6 people in the house most of the time, so plenty of sources for moisture generation.
I always thought 78F was too warm, until we lived with my father-in-law while building our house. He kept it at 78F and 42% RH, and it was very comfortable, almost too cool upon occasion.
Well, you got the system already and its working well. As you said its probably oversized for the house.
Now, what do you do to get that humidity down?
First, on the Tappan variable speed A/H. add in the humidistat option. If that doesn't help the humidity problem; has anyone suggested a whole house dehumidifier.
Not the most elegant solution but you already have the system installed and may be your best bet.