New Build HVAC proposal Need Some Help
I have been lurking here for the last 6 months and have learned much. I am building a 4800sf home in the Dallas TX area and it is now decision time on my HVAC units. I wanted to go geothermal, but i cant justify the cost (over double) vs. a high efficiency heat pump. I have had loads run by richard rue at energywisestructures.com
First a little about the project:
Wife and I + 4 kids in a 4850sf house near Dallas, TX
Stick built with .5lb open cell foam total encapsulation (cool attic) metal roof
Load was split into 2 units (one upstairs 2 ton one downstairs 4.5 ton) 6.5 tons total. I am considering splitting the downstairs into 2 units one for master suite and one for rest of living area.
Load Estimation via energywise
Downstairs: Heat 65550 btus Cooling 51467 btus
Upstairs: Heat 18358 btus Cooling 19718 btus
Based on winter indoor @ 70F outdoor 22F Summer indoor @75F outdoor 102F
I am looking at the Carrier Infinity Heat Pump 16 seer line and have been given these model numbers to look at:
Condensers M# 25HNA636A003 with a fan coil M# FE4ANF00300
M# 25HNA624A003 with a fan coil M# FE4ANF00200
These are 2 and 3 ton configuration as I am highly considering splitting the bottom into 2 systems. I tried to look these combos up at the ceedirectory.org and could only find 25HNA636A30 is this different than the A003 suffix? I found these not sure if this is correct though.
1250410 Active OEM INFINITY 16 PURON HP CARRIER AIR CONDITIONING 25HNA636A30 FE4AN(B,F)003+UI 34000 11.90 15.50 32600 8.60 18600 Energy Star HRCU-A-CB
1250413 Active OEM INFINITY 16 PURON HP CARRIER AIR CONDITIONING 25HNA636A30 FE4AN(B,F)005+UI 35400 12.40 16.20 33800 8.80 19000 CEE Tier 1 HRCU-A-CB
1250404 Active OEM INFINITY 16 PURON HP CARRIER AIR CONDITIONING 25HNA636A30 FE4ANB006+UI 35800 12.60 16.50 34200 9.00 19100 CEE Tier 2 HRCU-A-CB
882735 Discontinued OEM INFINITY 16 PURON HP CARRIER AIR CONDITIONING 25HNA636A30 FE4ANF002 33600 11.50 15.00 33000 8.50 18900 Energy Star HRCU-A-CB
1250407 Active OEM INFINITY 16 PURON HP CARRIER AIR CONDITIONING 25HNA636A30 FE4ANF002+UI 33600 11.50 15.00 33000 8.50 18900 Energy Star HRCU-A-CB
Seems that the air handler is different on these???? Can a 5 ton Handler go on a 3 ton unit???
The additional cost to go 3 units vs. 2 units (with 3 zones) is less than $1000 after rebates and not needing the zone controller. Plus duct work will be much easier. Is there any reason not to go 3 units (3+2+2 vs 5+2)?
Any insight to the best match of condensers and air handler match would be of great help as i want to be as efficient as possible without blowing the budget. I would like to stay 2 stage + variable speed for dehumidification purposes.
I have been advised by energywise NOT to get a ERV as i should have enough air changes in normal 6 person lifestyle. I would like to procede w/o one. Is this hard to retrofit if needed down the line?
Thanks again for your thoughts. I have to decide soon.
Last edited by hldr; 11-14-2008 at 12:17 PM.
Just found out that the $1100 per unit Carrier rebates are only good til 11/17.
Do these generally get extended or replaced as they expire?
Yes, less equipment - longer run times - much greater efficiency... Try to just use one unit instead of two or three. Let's face it, how often will you occupy 100% of this house? With zoning you can under size more! How likely is it you will ever be heating or cooling 100% of the space to design temps under worst case. Crazy to pay so much extra in equipment and energy cost for the 1/100th of a percent possibility.
What you are talking about sounds like way over sized! With open cell your infiltration will be non-existent. You'll have no in-cavety convective losses - and the roof load will be amazingly small. Don't build super energy star then size based on a 1990's house. You won't like the performance or bills of over sized equipment (with the exception of your duct work).
Smaller is better! Zoning allows bigger margin on the small side.
In regards to the 5-ton air handler with the 3-ton system, they do that frequently to get the SEER rating up. Many manufacturers use one air handler with a model number sized for say 5 tons at 13 SEER that would be rated for only 3 tons at 16 SEER.
If your kids are older, i.e. leaving the nest soon, and or this is going to be the last house your planning on living in, I'd bite the bullet and install the ERV now. It will be cheaper to have the installing contractor put it in while everything is accessible rather than trying to squeeze it in after the fact. If you are still convinced that you don't need one, have the contractor look at putting any neccessary wiring and space available to make a post occupancy installation.
What's your superheat?...."uh....it's good."
What were your pressures?...."uh, they were fine."
If I never here this again, I will die a happy man.
If you don't need one your house is too loose. Have him tighten it up.
Originally Posted by proto_moose
In a house you plan on staying in you want to need one. The equipment cost is fixed and will never be cheaper. Iaq will be MUCH better-pRticularly in keeping voc low in a new house. And doesn't it make sense to assume energy prices will go UP? Roi will go up with them.
Retrofit is usually much more costly-save energy out of the box. Get the fancy countertops later.
And they dn't apply to new construction homes.
Originally Posted by hldr
Zone the bottom floor,maybe the top too.Infinity zoning is tops!
ERV,yes,consider using it as the bathroom exhaust also,swithes for the bath with timers,and Inifinity Control,will also control it.
Here's one we did,ERV is the bath exhaust,plus Air Purifiers,might want to add them as well.
Last edited by dash; 11-15-2008 at 02:48 PM.
I also live in the DFW area. I have approximately 4,000 sq. ft. of conditioned space, and all I need is a 2 ton heat pump.
The cold attic is a good start. Also very important is to air seal the house, and shade the windows in the summer.
Add a fresh air duct to the intake on your air handlers. Have a blower door test done and fix any problems found.
I monitor the air quality in my house with a CO2 meter, but that is the engineer in me.
Do NOT skimp on the thermostats. I recommend and really like my Honeywell IAQ for comfort and humidity control. The ability to slow the variable speed blower for humidity control works extremely well without going with the extra cost of 2 stage units.
For my house, the extra cost of an ERV would take too many decades to recoup. In the hottest months, keeping my house at 74 degrees and 42% humidity cost me about $75 a month. An ERV would not change that enough to ever repay itself.
im still unclear about how to match the systems. A 3 ton unit with a fe4anb006+ui air handler seems odd but is the config that ahridirectory shows as being common. Isnt this too much blower for 3 tons?
Also what does the +ui mean on that handler?
Unfortunately due to layout of my home it isn't feasible to use one unit with zones. It might be possible to do 2 units (one master suite + one rest of house on zones). my master suite has 16k btu cooling and 18.5k btu heating with roughly 500 cfm need in each mode.
The manual j calls for 4.5 tons down and 2 tons up. I really thought this seemed low for 4850sf. since a 4.5 ton unit isnt available we are looking at a 5 ton for down or a 2 and 3 ton units.
Are we sure that the rebates wont work with new construction? my installer said it was $1100 per unit.
2 tons for 4000sf seems very impressive indeed. 2000sf per ton --- wow. are you a sip panel or icf home. almost all of our windows have shade or porch overhangs. sprayfoam + encapsulated unvented attic. hopefully we will be well sealed.
we do have 2 adults + 4 kids ages 5, 7, 9, 11. So, our home will be full for some time.
Just thinking from a design standpoint for the moment. Rather than an ERV, how about a fresh air supply ducted into the return of the air handler, and then a relief duct elsewhere in the house, sized smaller than the fresh air intake so the internal pressurization of the building's shell stays positive.
Control both via a carbon dioxide sensor. When CO2 levels approach a predetermined threshold, both the fresh air intake and the relief dampers cycle open. If the HVAC system is not running, the ECM blower in the air handler cycles on at the lowest possible speed. If the HVAC system is running, it operates at appropriate blower speeds, with the fresh air intake and relief dampers sized for maximum required air exchange.
Requirements for this system to be effective are a tight structure. There is the drawback of off-cycle fresh air purging in humid climates altering indoor humidity levels. Therefore a humidistat or thermostat with dehumidification capabilities would be required, which would bring the system on to counter any increase in indoor humidity levels, while providing greater quantities of required fresh air. Careful attention to structural air tightness, duct sealing, and thermal resistance of the structural envelope would be required for this strategy to work, along with smart controls, in order for the approach to not offset any hoped for energy management gains.
- Electricity makes refrigeration happen.
- Refrigeration makes the HVAC psychrometric process happen.
- HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.
A building is NOT beautiful unless it is also comfortable.
The unvented conditioned attic does solve many of the air sealing issues. How much heat gain are you getting in through your windows? If you don't know, HVAC-Calc is really worth the small investment to figure it out for yourself.
There is more than one way to make sure a house is air tight. A blower door test is one of the simplest. In my case, I was there for every step of the construction, did the air sealing myself, and I have tested it since then with my CO2 monitor. I have a fresh air intake into the return on my HVAC. Without that, I would have to open windows to keep the CO2 at a reasonable level.
I would think that the combination of the clothes dryer, bathroom exhausts, and kitchen exhausts would provide more than enough relief vents.
I was too cheap to go with ICF or SIPs. I do not think they are cost effective in our climate. The house is unconventional in design with conventional design methods. It is a stick built house with cellulose insulation, including R49 in the attic. I put the duct work / air handler in what some people call an unfinished basement. In reality, it is on a sloped lot and all above ground. Insulation is important, but the really important issues are the air tight construction, shading the windows, and keeping all of the duct work in conditioned space.
Originally Posted by hldr
Have them recheck their clcs,matching your building specs.
UI is the controler/stst,and a very good one ,has all if not more then the IAQ stat.
If he can do it,against Carrier rules,but saves you some money.