Heat Pump rule of thumb
Heat Pump rule of thumb
(OP)
is their a rule of thumb for a heat pump ton size required per square foot? Residential home in NC.
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Heat Pump rule of thumb
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Heat Pump rule of thumbHeat Pump rule of thumb(OP)
is their a rule of thumb for a heat pump ton size required per square foot? Residential home in NC.
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RE: Heat Pump rule of thumb
RE: Heat Pump rule of thumb
http://www.airdesign-hvac.com/sizing.htm
http://www.airdesign-hvac.com/howthey.htm
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FAQ731-376: Eng-Tips.com Forum Policies
RE: Heat Pump rule of thumb
RE: Heat Pump rule of thumb
I have posted this link many times before. There is free modeling software called eQUEST available at http://www.doe2.com/equest/. This software is made available courtesy of California's electric utility ratepayers and the California Public Utilities Comission. You can even get free training on the software in California through the electric utilities. Using the schematic design wizards is relatively easy and if you are familiar with modeling software it should only take you an hour or two. Since I use it a lot I probably could do a block load for this house in fifteen minutes. It is used in LEED assessments very often.
If you do decide to use it I would click on the "multifamily dwelling low rise" to use its default settings. There is no single family residiential since it is not intended for a residential tool.
RE: Heat Pump rule of thumb
Contractors in NW Florida use 600sf/ton, so if your east of the hills, I quess around 700sf/ton without doing a load calculation.
RE: Heat Pump rule of thumb
Heating load in the Southeast is approximently 2.5 times cooling load. So if you assume 3 tons for 1800sf home in Atlanta, assume your heating load will be around 90k btu/hr.
Rules of thumbs are just a guideline -- they're nice to compare your engineering calcs for comparison; then, you can rethink your assumptions to derive a professional calculation.
RE: Heat Pump rule of thumb
But I DO use a self imposed check of 550 - 650 sq.ft. per ton for residential condo calculations. It seems that the majority (Florida coast condo's excluded)of the condo's run upward of 800 sq. ft/ton per load calculations. While this is what the condo unit may require to meet the cooling load - at this value not enough air is being delivered to assure good air circulation throughout the space. That's when I will increase the tonnage by using the 550 - 650 number.
Andy W.
RE: Heat Pump rule of thumb
Sorry
RE: Heat Pump rule of thumb
Huh?!?!?
By your estimate, a 3-ton heat pump system would require as much as 90,000 BTU's of heating? That is a 69 degree delta T!! How you going to get that out of a heat pump? Gas Furnace maybe......
Heating is always much less than cooling here in the southeast . Best advise I can give is to size your supplemental heat for a 25 degree rise or 95 degree discharge. With this, you are covered even if the compressor fails.
Andy W.
RE: Heat Pump rule of thumb
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat Pump rule of thumb
For reference, on a typical home even when the outdoor temp dropped to -45C not one furnace ran continually. Mine ran ~1/2hour on the hour.
RE: Heat Pump rule of thumb
A lot of times when the southerners use gas heat, they end up using a GROSSLY oversized gas furnace, just so that they can move 5 tons worth of air.
When I was contracting in Canada, the most common size furnaces I sold for NEW construction homes was 60K and 75K, in both condensing and non-condensing models
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat Pump rule of thumb
One other interesting phenomena we're seeing is whole subdivisions without a single chimney...
All new homes are being built with a condensing gas furnance, and power vented water heater.
A little off topic but...whose reading this thread anyhow.
RE: Heat Pump rule of thumb
what is the delta T between 5 degrees ambient and 75 degrees indoor?
heat loads are based on 1% loads.
RE: Heat Pump rule of thumb
almost everyday.
If a 3 ton HP can provide 24k btu/hr of heat on a 10 degree day, the rest has to be made up in auxillary heat.
Think about it -- during the Summer the difference between ambient and indoor is around 20 degrees -- what is the difference between 70 degrees indoor & a cold winter day???
RE: Heat Pump rule of thumb
Big jump between the ice age returning and designing for 10F in Florida and saying a home with 2.5 tons of cooling needs 90,000 heat.
Ambinent temperature is a lot less significant in cooling, but what really matters is how sunny it is and how humid it is.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat Pump rule of thumb
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat Pump rule of thumb
R10 walls, R20 roof, R2 windows.
1800 ft2 home (assume 50 x 36) w/8'walls. 30% glass walls
Assume 40 deltaT (30F to 70F) (1% design condition)
Walls; Q = 1/10*1376*40 = 5505 Btu/hr
Roof; Q = 1/20*1800*40 = 3600 Btu/hr
Windows; Q = 1/2*412*40 = 8240 Bth/hr
Rough total: 17345 Btu/hr ... which is more than I would size any furnace in Florida for.
In summer the ambient contribution to cooling load is 1/2 (~8000 Btu/hr). which means the rest of the 30,000 Btu/hr cooling load is solar (and humidity).
I've ignored ventilation because 1)most of my projects use HRV's 2) This post was getting way to long anyhow. I've also guesses on R values... but even if you half the R values we've got a long way to go to 90,000 Btu/hr.
RE: Heat Pump rule of thumb
I'm sure they're smarter than anyone on this post(execpt me).
I also be my salary is well over 3 times yours abby :)
RE: Heat Pump rule of thumb
If you ever did a heat load you would not have to rely on something you read in a book.
If you in fact are up to writing an exam one day for a license, please keep this in mind. Only comment on matters that you have enough experience with to be deemed competent.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat Pump rule of thumb
I don't believe that your posts are quite within the spirit of forum. See FAQ731-376: Eng-Tips.com Forum Policies for more details although I don't know if any rules specifically address modesty.
I don't quite understand how salary size relates to the validity of a technical opinion.