Hello everyone,

I was working on a school model located in Lakeside, San Diego county.

The school has Bard wall mount heat pumps (capacity - 2 to 4 tons),

really old one. I got manufacture data of the old and new units for

replacement. The new units data has EER, IPLV and COP ratings. I would

prefer to use IPLV instead of EER rating in case of cooling to

calculate savings. The eQuest does have options for EER and SEER but

not for IPLV in the schematic design wizard. What should I do here?

Does it make sense to use IPLV instead of EER to calculate savings for

the Lakeside?

Thanks,

Amandeep Singh

Amandeeph:

As far as I am concerned, IPLV is a mythical number, like SEER. It is based on assumed levels of usage for a pumed annual usage. If your truly need part load curves, ask the manufacturer for the 75%, 50% and 25% points. You cannot evolve these four numbers out of a single mnumber (IPLV).

Amandeep:

?

I agree with John.? Actually, I believe IPLV is a somewhat new rating that applies to larger systems.? EER or COP are?much more accurate ratings.

?

I am confused about the SEER and IPLV ratings.? What temperature bin do they use to calculate these numbers?? It would seem to me that an AC system in the south would operate at a higher load throughout the cooling season than one in the northeast.? Of course, it would depend on how the system was sized.? An oversized system will operate at a much lower load ratio than a tightly sized system.

?

Does anyone know the formula?

?

Paul Diglio, CEM

All,

The ASHRAE Journal December 2009 Issue has a fitting article "A Closer

Look at Chiller Ratings" highlighting the problems of over-reliance on

IPLV/NPLV for use with chillers, and specifically what type of impact

climate has on these ratings. Lesson: be wary of these broadly applied

simplified ratings.

eQUEST won't allow you to input IPLV to describe a system, but you can

calculate it for the part-load and off-design performance curves that

eQUEST will use as defaults, and determine if the curves are suitable to

use in your case. Just don't be surprised though if the actual

performance based on your specific building and location ends up nowhere

near the IPLV performance.

Regards,

Jonathan M. Curtin, EIT, LEED(r) AP

eQuest automatically calculates part load performance based on the rated condition (COP in your case) and the performance curves that modify the power consumption based on temperature and part-load (and other factors for other equipment...water temperatures, etc.).

If you input IPLV where eQuest is expecting a COP, you'll be underestimating the power consumption from the units. These inputs will often be in the form of "Energy Input Ratio", or EIR for many types of eQuest equipment which is the inverse of COP.

If you need to verify the part-load performance that will be calculated, you can use hourly reports to verify that using the COP and default performance curves gives a reasonable result.

As others mentioned, the IPLV references a specific set of weather and load, applied to the piece of equipment. The average annual efficiency will vary based on your actual weather and load on the unit.

David

A colleague of mine has an answer about this below.

Regards,

Carolyn Balant P.Eng., LEED AP

Carolyn:

Short answer:

Amadeep should use SEER for his project. IPLV is used for chillers, but it is no better than SEER. I believe EER and SEER include fan power, but I am not positive. I know that IPLV does not include power for any peripherals.

Long answer:

EER (BTUH/watt) and COP (dimensionless) are rated at full load.

SEER (seasonal efficiency ratio) and IPLV are supposedly based on an entire "average" season of operation in a "typical" system, with a large number of assumptions about load profiles, outdoor temperature profiles, presence or absence of economizer cycles, and operating profiles. SEER is in BTUH/Watt, and IPLV is either in kW/ton or expressed as COP (dimensionless). The "V" stands for Value because, incredibly, the units of IPLV are ambiguous!

IPLV is generally used for chillers. It is based on:

1% of time at 100% load

42% of time at 75% load

45% of time at 50% load

12% of time at 25% load,

with different assumed condenser water temperatures at the various loads.

(There are published formulae for calculating IPLV with any arbitrary load profile. Unfortunately, and likely because of the ambiguity of the units, the authors used the COP form of the formula for kW/ton, and vice versa. Because COP and kW/ton are essentially reciprocals of each other, the formulae don't work. But that's another story.)

SEER is another ARI standard, presumably based on a similar load profile. I don't know what the profile looks like, because ARI charges $45 for a peek at the standard. And guess what...

Regards,

Jamie Smith P.Eng

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