Hello all,
we are going to use ASHRAE 90.1-2010 for our LEED v2009 project in Germany. One problem pops up recently. The cooling system we will use in the project is a split cooling system which uses a compressor to distribute the refrigerant through a piping network to multiple indoor units. You can find the chiller here if you are interested:
http://www.emersonnetworkpower.com/en-CALA/Products/PrecisionCooling/Dat...
The problem is in ASHRAE 90.1-2007, the efficiency of VRF cooling system was not covered in the mandatory provisions for LEED minimum energy performance, but in ASHRAE 2010 the minimum efficiency for VRF air cooled air conditioner of our size is 11.6. The ESEER value of our chiller mentioned above is 3.99. I guess there must be something wrong but I can't figure out where. I did some research, and found out that in Germany the efficiency (ESEER) of this kind of chiller is always around 4 to 6. How can it be that their efficiencies are all much lower than the minimum efficiency required in ASHRAE. Or is this kind of cooling actually not exactly the same as what ASHRAE describes, which means there is no requirement on the efficiency of our cooling system?
Thanks a lot.
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
July 19, 2016 - 10:52 am
1) The german ESEER most likely uses a different rating test proceedure. This is a rating value. It means the equipment is tested in the land at specified operating conditions and the results of those tests are weighted as per the proceedure chosen resulting in a single number rating value. A different rating proceedure will result in a different rating value.
2) A VRF system has nothing to do with a chiller. A chiller produces chilled water. A VRF system has indoor and outdoor units that work (usually) with refridgerant, i.e. something that changes phase from gas to liquid in the cycle.
3) chiller efficiencies are anywhere between 3.2 and 5+ depending on how they are back-cooled and other factors; VRFs differ widely...11 to 16. Again this all depends what kind of rating value and method is used.
Dandan Li
LEED AP1 thumbs up
July 20, 2016 - 12:10 pm
Hello Jean,
Thanks a lot for the input. Now I get your point. So actually what we have in project is not a VRF system, but a chiller system, which carries water instead of refrigerant. As you already said, chiller efficiencies are between 3.2 and 5+. What we plan to use in the project is a air-cooled chiller with cooling capacity from 340 kW to 1200kW, and also with built-in free cooling section. The efficiency:
ESEER = (EER@100% load × 0.03) + (EER@75% load × 0.33) + (EER@50% load × 0.41) + (EER@25% load × 0.23)=3.99
IEER=(EER@100% load × 0.02) + (EER@75% load × 0.617) + (EER@50% load × 0.238) + (EER@25% load × 0.125)=3.80
Does it meet the minimum requirement (mandatory provisions of ASHRAE) of this LEED credit? When I looked at the TABLE 6.8.1A in ASHRAE 90.1-2010, it seems really difficult for us to meet the requirement...Or did I use the wrong TABLE?
Thanks!
Maya Karkour
EcoConsulting871 thumbs up
July 21, 2016 - 5:10 am
Hello, I guess there is a problem of units. In the US, efficiency can be expressed in (BTU/h) / W. Whereas in Germany, it's dimensionless, W / W.
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
July 21, 2016 - 5:58 am
Unfortunately, the calculation you made it perhaps good for reference, but it's not as simple as you think. Every EER is a rating condition that depends not only on partload percentage of full load (at the rated full load condition), but also depends on other variables like outdoor and indoor air drybulb temperatures and humidities as well as supply and return water temperatures, volume flow rates, sensible heat ratio (and bypass factors). Don't try to calculate this. Get this from the manufacturer for the rated ARHI or whatever test proceedure aligns with the rating value. If they can't supply this then get the test data and simulate it with a program that is capable to simulate the equipment through the rating tests to deturmine the rating value correctly. Or get someone who knows how to simulate it, as not every building simulation expert knows how to do this.