Replydid the contractors do a load calc?
did you account for RH?
did you show your calc to contractors, so they could catch errors?
have you been comfortable when old system was running?
Regular Guest
A/C out - need to decide on new system NOW!! Opinions please
Hello all, I've been researching new HVAC system for one of the zones of my home in Dallas, TX. Good thing, as my AC went out today, so will likely replace unless it's a cheap fix. Current equipment is 3.5 ton, 15 years old, 10 SEER, R22.
Did a load calc for the area and it came out at just over 3 tons (39,581 BTU heat gain). Please look at systems proposed and let me know which you would recommend, given that system 2 is about 15% more than system 1. Could also go with a comparable Rheem system for about the same as system 1.
Both systems would include same install details including all new duct work, but use existing line set.
Liked both contractors, and both come highly recommended, so would be comfortable with either. Thanks in advance for your thoughts, as I'll likely need to pull the trigger on this in the next couple of days.
System 1 - 3.5 Ton
WESTINGHOUSE 3.5 TON 14.5 SEER SYSTEM (41,500 BTU COOLING)
- CONDENSER M# FS4BE042K
- HIGH EFFICIENCY COILS, M#C5BHX42CB
- 96,000 BTU FURNACE, M# FG6RA07216B
MANUFACTURER'S WARRANTIES: 10 YEAR ALL PARTS, PLUS WESTINGHOUSE "QUALITY PLEDGE"WESTINGHOUSE 3.5 TON 14.5 SEER SYSTEM (41,500 BTU COOLING)
System 2 - 3 Ton
Carrier two speed condensers model # 24ANA748A003.
Carrier variable speed two stage 80 % afue furnaces model # 58CVA090-1-16.
Carrier tin plated indoor evaporator coils model # CSPHP4812ATA.
Carrier Infinity controls model # SYSTXCCUID01-B.
Carrier EZ-FLEX merv ten rated filters model # EXPXXUNV0016.
Warranty:
Ten year parts and labor extended, ten year compressor part and twenty year heat exchanger part warranty.
Professional Member
did the contractors do a load calc?
did you account for RH?
did you show your calc to contractors, so they could catch errors?
have you been comfortable when old system was running?
harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!
Professional Member*
\Originally Posted by rhb4321
System 2 = Is a 4.0 ton NOT 3.0 ton.
Get the Carrier and hurry before your 1000.00 rebate expires on June 30,2008.
'Life begins with the journey each day'
Professional Member
Westinghouse in my oponion would be considered a builders model or second tier product. The weather is a little cooler do a little more research. Highly recommended referrals usually mean he has best price or he's a nice guy they don't automatically translate to top quality.
Last edited by nvr2old; 06-18-2008 at 08:24 AM.
Professional Member*
Don't oversize the equipment. Looks like you need a three ton and nothing larger by your calculations.
You oversize and you will have equipment short cycling with bad humidity control.
Beware of advice given by some guy on the Internet.
Professional Member*
Go with the 3 1/2 ton anything. As far as oversized, it would be so marginal, it wouldn't effect anything. Not only that. I'm 3 hours south of you and its hitting 100 degrees regularly. Your old one was a 3 1/2 ton and your load calc came out somewhere in between. You would have short cycling and possible humidity issues if you went to a 5 ton, probably even a 4. Doubtfully a 3 1/2. Talk to your contractor, they will guide you along.
God Speed, Jim. We'll miss you - 2-26-23
The Carrier is a 4 ton 2 stage 50/100 compressor. So in first stage it should have roughly 2.4 ton capacity.
How did your old 3.5 ton handle the cooling load over the years. Did it struggle sometimes, or did it cycle on and off on your normal hot days.
If it stuggled, he the Carrier 2 stage. If it cycled, the Westinghouse 3.5 ton.
Regular Guest
I actually did the load calc using HVAC-Calc and the pre-loaded settings for Dallas, TX, then had the contractors validate it. As to comfort, it struggles a bit during the hottest days, but I'm convinced that is as much my spaghetti duct work as it is the unit. When I do this, I'm going to re-locate the unit to make more direct duct runs; that's included in the pricing.
Any concerns over the reciprocating compressor in the Carrier?
God Speed, Jim. We'll miss you - 2-26-23
No, its a good compressor.
So your increasing to a 4 ton then.
What did the load calc say for sensible, and latent load.
Regular Guest
Here's the HVAC-Calc design conditions and summary report for the zone in question:
Design Conditions: Dallas
Indoor: Outdoor:
Summer temperature: 72 Summer temperature: 105
Winter temperature: 70 Winter temperature: 20
Relative humidity: 55 Summer grains of moisture: 93
Daily temperature range: High
Sensible Gain: 36,222
Latent Gain: 3,359
Total Gain: 39,581
I did not use any "safety margin", just went with the Dallas settings from CALC.
Think the Carrier is a better system, but worried about over/under size with it, as the Infinity doesn't have 1/2 tons......
Final wild card thought: what about the Westinghouse IQ? This is the most lived in part of the house, so might consider spending more to ensure comfort.....
God Speed, Jim. We'll miss you - 2-26-23
The IQ, may be a better choice for you. It should mod down to what you need under most of the load conditions you'll have.
Regular Guest
The traditional load in Dallas has been a design of 100*F. 105 is high as a design temperature unless it is a year like 1980.
You show a sensible of 36,222. This is a load, and not an equipment selection. When you match sensible to sensible, you may find that a 4 ton equipment is closer, if 105* is the design point. That's why the question of were you content with your 3.5 ton.
When the outside temp goes over 95, then you have to derate the outside unit. When the inside is 72 and not 80 then you have to adjust the evaporator. Minor adjustments to be sure, but Manual J is only a beginning point for equipment sizing.
Regular Guest
Oops, posted the one where I DID use a "safety factor". The one using CALC design conditions was a "bit" lower, but still in the "which way do I go" range.
I am interested in some of the comments regarding the Westinghouse system, as AHRI lists Carrier as the weaker EER and Btuh of the two. I realize that the controls are different, but couldn't I get the same dehumidifying effect with a variable speed furnace and Honeywell VisionPro stat? Still trying to learn what's what......
Regular Guest
Manual J is considered to already have a safety factor built in.
105*F design temperature instead of 100*F adds a half-ton. Since 100* is the 0.4% point, it is considered an extreme point in terms of time temperature exceeded.
Winter design temperature is normally taken as 17*F.
God Speed, Jim. We'll miss you - 2-26-23
A non IQ Westinghouse with VS drive will not dehumidify as well as A 2 stage Carrier 50/100 will with the Infinity control. The carrier will have better blower control.
Thats why it cost more. Plus the Carrier name.
Regular Guest
You guys are great!! Thanks for all of the advice. My trusted HVAC repair guy came out today and found a small leak in the condenser coil, so dumped in some R22 to get us working again until I can figure out what to do. So I've got a little breathing room, but still need to replace the system asap. SO that means I'm gonna keep asking questions....
My Westinghouse dealer is going to quote an IQ system, so will see how painful that option would be....otherwise, it sounds like the consensus is to go with the Carrier system, even though it's a lower EER (which is what I understand that I should really care about for energy efficiency, being in Dallas). So, help again; is the Carrier more about comfort?? Thanks again!!!
God Speed, Jim. We'll miss you - 2-26-23
You set your thermostat to a temp that you are comfortable at, correct.
If you only set it as cool as low as needed so as not to die from heat stroke or exhaustion you don't need a system to provide comfort.
Regular Guest
Sorry, don't understand your question......
God Speed, Jim. We'll miss you - 2-26-23
Are you buying a system just to cool the air. Or are you buying a system to keep you comfortable.
AOP Committee/Professional Member*
Earlier, you indicated the existing duct system was inadequate.You guys are great!! Thanks for all of the advice. My trusted HVAC repair guy came out today and found a small leak in the condenser coil, so dumped in some R22 to get us working again until I can figure out what to do. So I've got a little breathing room, but still need to replace the system asap. SO that means I'm gonna keep asking questions....
My Westinghouse dealer is going to quote an IQ system, so will see how painful that option would be....otherwise, it sounds like the consensus is to go with the Carrier system, even though it's a lower EER (which is what I understand that I should really care about for energy efficiency, being in Dallas). So, help again; is the Carrier more about comfort?? Thanks again!!!
If the duct system was only delivering 2.5 or 3-ton of airflow through the coil that is what your 3.5-ton unit would deliver.
It is extremely important that you are renovating the duct system.
However, I would look at where I could reduce the heat-gain/heat-loss so you could use a 3-ton condenser. You could always do more reductions if it didn't handle it well enough.
I checked the Dallas summer conditions & it indicated 31% Relative Humidity, which means it should deliver a high sensible ratio. I know there are times when humidity will be high.; that is when you need longer run times.
If you chose equipment & contractor wisely, you may save enough to do the reduction in heat-gain which beats paying more for supposedly higher SEER Ratings, etc.
The decision is yours, if it were me, I would thoroughly analyze all the options!
http://www.udarrell.com/airconditioning-sizing.html
- Darrell
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