Heat Pump sizing for major renovation
First post (to this forum at least) and I have educated myself significantly over the last few weeks. Big thanks to all of you folks that help the rest of us out.
We're in the middle stages of a major, whole house renovation of a house in Chapel Hill, NC. We plan on being in the house 10-15 years so we are really focusing on trying to do things right from a quality perspective and not always let budget dictate the decision.
The completed house will be a ranch with a finished basement plus a MBR over the garage. Sq footage is approximately 2235 up and 1731 down in the basement. The basement is mostly underground with only one wall allowing for walkout. We are replacing all windows with highly efficient ones and are planning on spray foam insulation for the main floor. It's TBD whether the attic is a conditioned space or not. All ductwork is new as is all HVAC. This house was completely gutted and will pretty much be completely new from the foundation out.
We've received quite a few quotes for the HVAC and have settled upon a company who has quoted us heat pumps from American Standard as part of a matched system with VS blowers on the indoor air handlers and dual zone for the MBR over the garage. Thermostats are the 8000 series by Honeywell. They also will install an outside air duct and damper system for ventilation due to the spray foam insulation.
First quote was for a 3 ton system (Heritage 18) upstairs and a 1.5 ton system downstairs (Heritage 15). At first glance i thought that was a bit overkill so I asked for a quote for the exact same setup except with the Heritage 16 up and the Heritage 14 down and the price was only about $1000 different between the two.
So, my questions:
1. I understand SEER but also from reading here see that EER is the more important value. Anyone know where i can find the EER values for AS?
2. For the mostly negligible price difference, what would you do? I'm not against spending the extra $$$ but am nervous about oversizing the system. I just don't want to assume that bigger is always better.
3. Thoughts on making the attic a conditioned space?
For those of you that live in the South, you know that humidity control is very important and since we're replacing everything, I don't want a humid house. It also doesn't get that cold here so i would think my biggest concern is humidity.
Any comments are appreciated, i'm an electrical engineer and am astounded by the many different options available with HVAC today. Hats off to you guys that can keep up with it. ;-)
I appreciate it.
www.ahridirectory.org tells SEER, EER, HSPF and capacity. Most Trane pumps are light on heating capacity except the new R410a version of the XL15i. Look at all numbers when deciding.
Friend of mine is a foamer and he swears by foaming the undersized of the roof to keep the attic cool. In his house, the attic will run around 10° above the house temp he says. Otherwise it can hit 150° in a hot summer month and this super hot air will penetrate your flex ducts and kill lots of your cooling. Most flex is about R4 so if you have 55° inside and 150° outside, an awful lot of that heat will warm the cold air. I saw one house so bad that over 1/2 of his 3 tons for upstairs was lost to attic heat penetrating.
Who sized the equipment? It certainly doesn't look oversized so apparently whoever did knows how to handle an extremely tight house. If you want humidity control, I'd want the 900 series Trane stats which is the Vision Pro IAQ model. Request that dehumidify on demand feature be hooked up on the variable speed air handlers. That way in mild weather if humid, the blower slows to suck extra humidity out. The 8000 series won't do that. Also note that the XL16i on low doesn't do near the job of dehumidifying as their single stage counterparts so personally I wouldn't spend a bundle on it. Many would disagree however.
1- American Standard's website should list EER...untrusting soul that I am..I use www.ari.org you will need model numbers to access this info. But it is unbiased.
2-I would spend some of that $$ and have a blower door test to pinpoint the leakage areas of the house and make the house tighter before conditioning it.
Once the sealing is done then have hvac company do a load calculation on the house using the verified infiltration numbers, correct insulation values, window types etc.
Bigger is better thinking will eat your lunch here.
Correctly sizing the system will save you in utility costs, upfront costs, and in many cases Dr. costs.
Seal it up..size it right..and dehumidify.
3- attic as conditioned space...boy I don't even know if I want to go there!
Maybe later when I have a little more time. (after all-- YOU asked for my thoughts..
most of these folks know better..LOL!)
Best of luck with your project.
The cure of the part should not be attempted without the cure of the whole. ~Plato
mh in nc
Go to ARI CEE HVAC Directory for HPs. It will show you most matched systems that give performance metrics of brand, HP condenser, inside air handler, as well as SEER, EER, HSPF, cooling BTUs, heating BTUs both at 47 degree and 17 degree outside temperature for various sizes. Certainly, Am Std HP systems will be listed.
First of all I would not hesitate to consider foaming your attic. I did mine last spring and I believe it is the best money we have spent on this old farm house. I measured attic temps after the foaming and found it about 10* higher than the living area of the house - and that was near the top of the attic, the warmest area. Before the foaming attic, temps were around 130*. Put about 50 CFM of air flow up there and humidity will not be a problem.
To control humidity in the house you need long run time of your cooling equipment. The best way to do that is for an inverter driven compressor that will change speeds to meet the changing load of your home and allow it to have long run times. These system are running at low speeds much of the time and providing unmatched dehumidification.
Inverter technology has been in use in other parts of the world for years and has been refined to the point that it is currently the top of the heap for comfort systems. Currently, only one U.S. manufacturer, Nordyne, has moved in that direction, but there are many other companies to choose from. Daikin VRV-S, Mitsubishi City Multi, Sanyo Eco-i Mini, all make fully variable inverter driven multi-zoned units that are extremely quiet, very efficient, and provide unmatched comfort.
These manufacturers are often thought of as being makers of mini-splits, but these are NOT mini-splits, rather full split systems. These are smaller versions of large commercial systems. They are often referred to as VRV or VRF systems.
These are fully inverter driven systems that have a single outdoor unit that can have up to eight or nine indoor units connected. The air handlers are small allowing them to fit in tighter spaces to create zones as needed. They also have ductless indoor units if that would work better in a particular space.
Since each air handler would have its own ducting this eliminates the need for specialty designed and installed elaborate over sized zoning duct work to handle multi zones with dump zones and the like. With the typical zone systems you would still be running a large compressor even when a small zone was the only one calling. With these systems the compressor slows down in speed to meet the load and can run as low as 25% of the rated capacity (a four ton unit running at one ton when the load is light and dehumidification is needed). The indoor units also modulate to meet the load.
Most of the manufacturers have many different types of indoor units (Sanyo, for example, has six different types of indoor units both ducted and ductless with seven different capacity ratings starting as low as 7,500 BTU and going up to a 4 tons) that can be connected to the outdoor unit. A single control tucked away in a closet will control all the units with only a small sensor the size of a match box in each zone. Having multiple zones will provide the greatest comfort within the home and increases the efficiency of the overall system.
Capacity range is three to five tons with heating capacities that can not be matched by any typical US system. You may well not need any supplemental back up heat. Can't really oversize them as the compressor slows down to meet the load and a little over sizing will provide you with reserve capacity for those rare times when it is really needed.
These systems do not have SEER rating due to all the different combinations but can be compared on an EER and COP basis. EER ratings are in the 11 range at the nominal rated capacity, but go up to about 20 EER in part load conditions. Daikin claims with proper installation, equipment life should be 20 - 25 years.
With the attic foamed you may be able to use a single four ton unit.