SEER, COP and HSPF
Hatherly
| Posted in GBA Pro Help on
I am trying to come to grips with SEER, COP and HSPF.
Is this correct:
SEER is BTU cooling / watt hours needed. So divide this number by 3.412 to get the COP. Thus a 16 seer unit would have a COP of 4.7 or so.
HSPF is BTU heat produced / watt hours needed. So take a heat pump with a HSPF of 10, which is supposed to be pretty good and divide that by 3.412 = a COP of 2.9.
Have I done that correctly and, if so, are there heat pumps that do better than a 10 out there?
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Replies
Amanda,
I think you are trying to develop conversion factors for rating systems that are not directly comparable. According to notes I copied a while back (unfortunately I failed to note the source):
"Both the COP and EER values for groundwater heat pumps are single-point (valid only at the specific test conditions used in the rating) values only. This is in contract to the seasonal values (HSPF and SEER) published for air-source equipment. COP and EER are not the same as, or valid for use in comparison to, SEER and HSPF."
Thanks Martin. I got the idea that you could compare SEER and COP from the Building Science website article on Ground Source Heat Pumps where it says: "The conditions for the standard SEER test are a rather unrealistic 80 F indoors and 82 F outdoors: hence the temperature “lift” is small and so advertised SEER rating can often be artificially high -models with SEER=19 or a COP of 5.5! are now available."
I divided the 19 by 3.412 and got 5.5 so figured it must be the same. I think the statement may have meant to be sarcastic and I missed the point!
Amanda, yes, you can do the calculation you described and get a number for COP. What Martin is saying, though, is that that COP is not directly comparable to the COP that the manufacturer will tell you because if you divide SEER or HSPF by 3.412 Btu/kWh, you'll end up with a COP averaged over the whole heating or cooling season. The manufacturer's COP will be an instantaneous value.
When you dive into the details of SEER and HSPF, you'll find a lot of problems with them. The quote you mentioned above points out the efficiency inflation due to artificial test conditions, but the way the seasonal average is generated is problematic and the failure to take into account latent versus sensible cooling. Instantaneous values are, in my opinion, a better way of comparing one piece of equipment to another.
Amanda, SEER & EER are related to the cooling/AC side of heat pump (or AC) and HPSF/COP are related to the heating side of a heat pump. The SEER & HSPF numbers are supposed to be a seasonal or average of an entire season. The EER & COP are a "snapshot" at a given outdoor temperature. EER's are rated at 95 deg(F) and COP's were rated at 47 & 17 deg(F). When I entered the HVAC industry in 1984, the EER & COP were the standards. At some point, the good ol' govt. decided that the seasonal factors were of more use so we switched to SEER & HSPF. Now the tide is starting to turn back the other way. Many standards now look at muliples of these such as the $1,500 tax credit looks at SEER, EER & HSPF. I always did like the COP because I was taught that a COP equated to a ratio of for every dollars worth of electricity that was consumed, you got $X dollars worth of heat. An electric resistance heater such as an electric furnace or supplemental heater on a heat pump has a COP of 1.0 You can find all of the ratings for each system (except COPs) at http://www.ahridirectory.org It is also best to keep in mind that no rating can apply to just the outdoor unit, it has to apply to an entire system (both indoor & outdoor). Also, many manufacturers use a "trade name" on particular line of outdoor units such as an XZ18. Don't be mislead by this number. The number such as 18 may only mean that one system in that line gets that SEER rating and it doesn't apply to every size and match-up in that line. Hope this helps.
Thanks everyone for your answers - it's all much clearer to me now.
Energy Efficiency Ratings
EER (energy efficiency ratio) is a measure of how efficiently a cooling system will operate with 80°F 50% RH indoor and 95°F outdoor. A higher EER means the system is more efficient. The term EER is most commonly used when referring to window and unitary air conditioners and heat pumps, as well as water-source and geothermal heat pumps. The formula for calculating EER is:
Btu/hr of cooling at 95°
EER = ________________
watts used at 95°
Because of the ratio of BTU/watts, an EER of 3.412 means 100% efficiency
SEER (seasonal energy efficiency ratio) measures how efficiently a residential central cooling system (air conditioner or heat pump) will operate over an entire cooling season. The SEER of a system is determined by multiplying the steady state energy efficiency ratio (EER) measured at conditions of 82°F outdoor temperature and 80°F 50% RH indoor entering air temperature by the “Part Load Factor” (PLF) of the system.
seasonal Btu of cooling
SEER = ___________________
seasonal watt-hours used
By federal law, every central split cooling system manufactured in the U.S. today must have a seasonal energy efficiency ratio of at least 13.0 (or 381% efficiency)
Formulas for the approximate conversion between SEER and EER or COP in California are:
SEER = EER ÷ 0.9
SEER = COP x 3.792
EER = COP x 3.413
SEER of 13 is approximately equivalent to a COP of 3.43, which means that 3.43 units of heat energy are removed from indoors per unit of work energy used to run the heat pump.
The relationship between SEER and EER is relative depending on where you live because equipment performance is dependent of air temperature, humidity, and pressure.
If you live in the higher humidity of Georgia, it is better approximated by:
SEER = EER ÷ 0.80 due to the much higher humidity
COP (coefficient of performance) is the measurement of how efficiently a heating or cooling system (particularly a heat pump in its heating mode and a chiller for cooling) will operate at a single outdoor temperature condition. When applied to the heating modes of heat pumps, that temperature condition is usually 47°F. The higher the COP, the more efficient the system. COP can be calculated by two different methods. In the first, you divide the Btu of heat produced by the heat pump by the Btu equivalent of electricity that is required to produce that heat. This formula is stated:
Btu of heat produced at 47°F
COP = _________________________
Btu worth of electricity used at 47°
The second formula is most frequently used to determine chiller efficiency. Using this calculation method, you would divide 3.516 by the number of kilowatts (kW) per ton used by the system. This formula is stated:
3.516 (1 ton/kW)
COP = ______
kW/ton
HSPF (heating seasonal performance factor) is the measurement of how efficiently all residential and some commercial heat pumps will operate in their heating mode over an entire normal heating season. The higher the HSPF, the more efficient the system. HSPF is determined by dividing the total number of Btu of heat produced over the heating season by the total number of watt-hours of electricity that is required to produce that heat. The formula is written:
Btu of heat produced over the heating season
HSPF = ___________________________________________
watt-hours of electricity used over the heating season
Most heat pumps installed have HSPFs in the 7.0 to 8.0 range, meaning they operate with seasonal efficiencies of anywhere from 205% to 234%. (To convert the HSPF number into a percentage, you just divide the HSPF by 3.412, the number of Btu in one watt-hour of electricity.)
Sorry about the formatting problems with the quotient equations. One of the limitations of this forum.
Thanks for such a detailed answer. What is an "entire normal heating season" that the HSPF is measured for? Is it for a specific climate zone or number of HDD or ? I would think that how that is calculated would have a big effect on the real HSPF for where you live.
HSPF is calculated for an average heating season. To convert the rated HSPF to a more accurate number for your climate, use this spreadsheet: http://www.eia.doe.gov/neic/experts/heatcalc.xls
It seems that all numbers are for climate zone 4.
Most Pioneer spec sheets just show HSPF. (spec sheets on amazon.com)
One shows HSPF4
One shows HSPF4 and HSPF5.
Comparing 6 models in the last spec sheet shows that zone 5 HSPF performance is about 83% of zone 4 performance.
I wonder if someone has a similar data for other brands, models and climate zones because a 17% difference is quite high. Installing those units in zone 1 or 8 will give even greater performance differences.
Yeah, I'm fully aware that even within a climate zone the differences can be significant, but a rough guide might be useful.
Tony,
The map below shows HSPF values in different climate zones for equipment rated with a HSPF of 7.8.
In Minneapolis, the HSPF of the equipment drops to 4.6.
In Miami, the HSPF rises to 10.3.
If you live in the continental United States, you can use this map to estimate a realistic HSPF for your equipment. (First, calculate the percentage variation from 7.8. For example, if you live in Minneapolis, the map tells you that equipment will have an HSPF that is only 59% of the nameplate rating, since 4.6 is 59% of 7.8.)
To read more on this issue, see the paper where the map comes from: Climate Impacts on Heating Seasonal Performance Factor (HSPF) and Seasonal Energy Efficiency Ratio (SEER) for Air Source Heat Pumps.
.
Tony,
One more point about the map I just posted: the map was developed for conventional American air-source heat pumps connected to ductwork. It was not developed for inverter-based ductless minisplits.
I would be cautious in using the ratios show on this map to draw conclusions about the performance of an inverter-based ductless minsiplit.
Interesting map Martin,
New York: 6.6/11
HSPF=9
6.6/7.8*9=7.6
The Pioneer WYS009AMFI17RL specs state:
HSPF4 = 9
HSPF5 = 7.6
The numbers seem to check out with that minisplit. Perhaps random luck because HSPF4 is supposed to be zone 4 and NY is in zone 4; so I wouldn't expect a correction.
So what would be the adjustment to the region 4 HSPF rating for ductless minisplits in the NYC area (right on the border of climate zone 4 and 5)? No adjustment at all? Hspf x .85%?
And is “region 4” the same thing as climate zone 4?
Thanks.