Hi All,
G3.1.2.1 in ASHRAE 90.1 says that "Where efficiency ratings, such as EER and
COP, include fan energy, the descriptor shall be broken down into its
components so that supply fan energy can be modeled separately."
However, I am a little unclear as to which baseline systems this applies to.
It seems that it would apply to systems 1 - 2, and not to systems 3 - 8?
Thanks,
--
Karen
Classification: UNCLASSIFIED
Caveats: NONE
Quick question. (Looking for a short and sweet response) Is EA credit 4
likely to be achieved using equipment using R-410a.
I have the equations, but I haven't run through them yet.
Shooting from the hip, is it impossible, unlikely, 50/50, very likely, or a
sure thing to earn EA credit 4 with R-410a.
[I have two projects, one using water to water heat pumps with a geothermal
well field, and the other is a 10 ton dx system.]
John Eurek
Classification: UNCLASSIFIED
Caveats: NONE
I've always found that you have a tougher time achieving this credit with smaller units, since they have more refrigerant per ton. But it is not out of the question...you really have to run the calcs to be sure.
If you have a chiller system, or large packaged RTUs, much easier time, although you still need to make sure the manufacturer's rep doesn't oversize the refrigerant coil to achieve the highest efficiency (and bump you over the allowed 100 refrigerant impact per ton).
James Hansen, PE, LEED AP
Hi Karen,
My understanding is that the statement will apply beyond system 1-2.
Whenever a HVAC system is defined in EER, it is necessary to separate supply
fan energy from cooling energy.
Supply fan energy = (gross cooling - net cooling)/3.413
and
COP = gross cooling /[(total input power - fan power) x 3.413]
Does it make sense?
Regards,
Cheney
Hi Eurek,
The answer to your question is VERY LIKELY.
Why?
* Since R-410a will have 0 ODP and relatively small GWP (1890). Eventually
the equation is decided by only LCGWP, since LCODPx10^5 will be 0.
* My personal feeling is that Rc (Refrigerant charge) is critical in your
case. The range is from 0.5 to 5 lbs of refrigerant per ton. The smaller the
better.
* Considering multi types of equipments, as long as your averaged LCGWP is
less than 100, you will be safe.
As suggested by James, you will have to run the calculation to be sure.
--
Regards,
Cheney
My experience has been the same as James - the smaller units typically
have more of a problem, particularly RTUs less than 10 tons. The
refrigerant charge is high compared to the maximum allowable to get a
total Refrigerant Impact per Ton <100.
Also, I just ran into this on a project as well - there are
"supercharged" chillers on the market that also have high charge-per-ton
numbers.
See Page 210 of the LEED-BDC reference guide for a table showing the
maximum refrigerant charges for typical refrigerants. For RTUs, 15-year
life, you have to be less than 1.98 lbs/ton and the last I remember only
Trane had a unit at that low of a charge and still met ASHRAE 90.1
minimum efficiencies.
Jeremy R. Poling, PE, LEED AP+BDC
Agree with all the previous comments; I'll also point out that split systems can be tough if there are long line-sets.
Aaron Dahlstrom , PE, LEED(r) AP
A clarification:
My question pertains to baseline models, with baseline systems.
--
Karen
Karen,
A 15-ton packaged rooftop single-zone system having an EER of 8.6 (COP of 2.5) is
specified for a building. The following table gives the design specifications. How should
this be modeled?
Equipment parameter Value
Net Cooling Capacity (Btu/h) 174,000
Total Packaged Unit Input Power (W) 20,128
EER 8.64
Gross Cooling Cap (ARI conditions) 182,000
A
The supply fan power is the difference between the gross and the net cooling capacity.
Supply Fan Power = (182,000 - 174,000 Btu / h) / 3.413 Btu /W h = 2343 W
the condenser into the airstream in Btu/h per Btu/h of electrical power input is:
COP = (182,000 Btu / h) / {(20,128 - 2343 W)* 3.413 Btu / W h } = 3.0
Some simulation programs use an energy input ratio (EIR), which is 1/COP. In this case,
the EIR for this piece of equipment would be 1/3 or 0.333.
--
Sam Mason
Sam
Great example. Would you kindly provide a detailed citation, so it is
recorded in the archives.
Thanks
Arpan
Hi Sam,
I guess my question is the definition of "packaged" for the baseline system
case. Systems 1 and 2 are very clearly packaged systems, with relatively
low fan power. The fan power calculation reflects this, with much lower fan
powers for these systems. However, systems 5 and 6 are called "packaged"
systems, but these systems typically serve a large portion of a building
with more extensive ductwork and higher fan powers (reflected in the fan
power calculation), subtracting out fan powers from these systems and
manipulating the EER of these systems results in very high EERs (upwards of
18???).
It is unclear to me which air conditioners listed in section 6.8 have a
rating which includes fan power and which do not. I am assuming that where
different "single package" and "split system" EERs are given, that the first
includes fan energy while the second does not.
Anyway, it seems that to model baseline systems, the simplest approach is to
choose the split system EER (if listed) in section 6.8, and calculate the
fan power according to the G3.1.2.9 guidelines. Therefore, the only time
you would have to do the calculation mentioned by Sam is for a proposed
design system where the fan energy is included in the EER.
--
Karen
Mr. Sam is referencing/providing:
User's Manual for ANSI/ASHRAE/IESNA Standard 90.1-2007
Example 11-C "Calculating COP for Compressor and Condenser"
(Found on page 11-18)
NICK CATON, E.I.T.
Karen,
Since minimum cooling efficiencies in ASHRAE Section 6 are given for ARI
rating conditions, we need to use fan power at ARI rating conditions to
calculate the baseline EIR. You can get fan power at rating conditions for
different types of systems from AHRI website, or simply trust the attached
document that is included in eQUEST documentation. After calculate EIR for
the baseline, I use G3.1.2.9 to determine the fan power.
Maria
Hi Karen,
Apologies if I haven't been following closely enough, but I think you
may be unnecessarily complicating the issue for yourself... if in doubt,
turn to the 90.1 glossary (section 3) regarding whether the efficiency
metrics are/aren't inclusive.
EER is a simple ratio of total input power to net cooling capacity. It
includes fan power. SEER is the same idea, only it's weighted over a
"normal" annual period. Again it includes fan energy.
While pulling the (calculated) baseline fan energy out of the prescribed
EER/SEER values may result in "unrealistic looking" efficiencies, that's
normal because fans are a big part of energy used by packaged equipment!
Put simply and correcting your last statement: All Appendix G baseline
model system types require fan energy calcs. These energies can be
subtracted from the "fan-inclusive" EER/SEER efficiencies prescribed in
Section 6 to determine cooling EIR figures.
Hope that helps!
NICK CATON, E.I.T.