[Equest-users] Chiller Curves

[Robby Oylear]

Hi Rob,

Part 2 of the Energy Design Guide resources program on HVAC Simulation goes
into detail on how to create custom chiller curves.  The guide can be found
here:
http://www.energydesignresources.com/media/2654/EDR_DesignGuidelines_%20HVAC_Simulation.pdf

The thing that trips a lot of people is that EIRFPLR is actually a ratio of
power draw, not efficiency.

For example:
EIRFPLR (50% PLR) = kW (50% PLR) / kW (full-load)

*Robby Oylear, LEED**®** AP BD+C*

*Mechanical Project Engineer*

*Energy Analyst*

* *

*D* 206-788-4571 | *C* 206-354-2721

*www.rushingco.com* <http://www.rushingco.com/>

On Wed, Jul 20, 2011 at 1:20 PM, Carol Gardner <cmg750 at gmail.com> wrote:

> Hi Rob,
>
> It looks like you all ready solved your problem, which is good, but I'm
> going to send you a comment anyway.
>
> When I create a curve, I always use "raw data points" instead of
> "coefficients". The reason I do is that I can always obtain them and I don't
> have to worry about making a calculation mistake because eQUEST takes the
> raw data points and calculates the coefficients for me. If I want to see
> what they are, I can look in the .bdl file.
>
> The only trick to raw data points is that for everything except
> refrigeration compressors the dependent, in this case PLR, needs to be
> normalized to either the ARI design, or the actual design if it is
> different.
>
> So for your chiller curve you would input: Independent    Dependent
>
> 1.0                     1.0
>
> 0.75                   0.7356
>
> 0.50                   0.6643
>
> 0.25                   0.582
>
> Anyway, that's my 2 cents.
>
> Carol
>
> On Wed, Jul 20, 2011 at 10:24 AM, Rob Hudson <rdh4176 at gmail.com> wrote:
>
>> Prior to your response, i got a little impatient and found some of your
>> past articles in the archives after a lot of digging.
>>
>> I found out that the EIR equation is actually a % of the EIR that needs to
>> be taken into account.  So the equation should output a value from 1 to 0 to
>> multiply the design rated EIR by to get the usage at that part load.  there
>> was a method that i found that, when the manufacturer doesn't provide you
>> with enough to populate all three of the custom curves, you can simply use
>> the EIR f(PLR) curve, which i did and got the results i expected to see.
>>
>> Thanks for your response, both past and present.
>>
>> Rob
>>
>>
>> On Wed, Jul 20, 2011 at 1:06 PM, Nick Caton <ncaton at smithboucher.com>wrote:
>>
>>>  Hi Rob!****
>>>
>>> ** **
>>>
>>> Well to start, let’s not assume every chiller out there MUST be more
>>> efficient than the default curve at every point.  Better to assume they can
>>> and should differ.****
>>>
>>> ** **
>>>
>>> With that disclaimer out of the way,  you have noted your coefficients
>>> generated for your custom PLR curve should produce a lower correction factor
>>> at 25% (confirmed in the Var 9 column you attached).  ****
>>>
>>> ** **
>>>
>>> What I think you’re missing is that there is indeed more than one
>>> correction factor being calculated every hour, and more than one curve in
>>> play to produce those factors that you need to consider.  The extra column
>>> you chose to include in your spreadsheet hints at this (Var 10).****
>>>
>>> ** **
>>>
>>> Recommended DOE2 reading that should fill in these specific gaps for
>>> you:  Volume 2: Dictionary > HVAC Components > CHILLER > Chiller Energy
>>> Consumption****
>>>
>>> ** **
>>>
>>> There much further discussion on this topic in the archives as well, if
>>> you just can’t get enough ;).****
>>>
>>> ** **
>>>
>>> ~Nick****
>>>
>>> ** **
>>>
>>> [image: cid:489575314 at 22072009-0ABB]**
>>>
>>> * *
>>>
>>> *NICK CATON, P.E.***
>>>
>>> SENIOR ENGINEER****
>>>
>>> ** **
>>>
>>> Smith & Boucher Engineers****
>>>
>>> 25501 west valley parkway, suite 200****
>>>
>>> olathe, ks 66061****
>>>
>>> direct 913.344.0036****
>>>
>>> fax 913.345.0617****
>>>
>>> www.smithboucher.com* *****
>>>
>>> ** **
>>>
>>> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
>>> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Rob Hudson
>>> *Sent:* Wednesday, July 20, 2011 6:23 AM
>>> *To:* equest-users at lists.onebuilding.org
>>> *Subject:* [Equest-users] Chiller Curves****
>>>
>>> ** **
>>>
>>> I have a new Chiller Curve question/situation.  I have created a custom
>>> chiller curve for the EIR = f(PLR) as a cubic function using the following
>>> data inputs:****
>>>
>>> ** **
>>>
>>> 1         .3313****
>>>
>>> .75      .2437****
>>>
>>> .5        .2201****
>>>
>>> .25      .1928****
>>>
>>> ** **
>>>
>>> From my understanding, the chiller curve seems correct.  However, when i
>>> create a hourly report summary for the Corrected Chiller EIR and compare it
>>> to the default EIR equation for this entry, i get 0.034 for the default and
>>> 0.072 for my curve at 25% ratio.  Why is it that the default is better than
>>> my curve?  I have looked at the equation for the default entry and got the
>>> following equations:****
>>>
>>> ** **
>>>
>>> EIR = a + b x = c x^2****
>>>
>>> a = .04812248****
>>>
>>> b = .69573420****
>>>
>>> c = .23493889****
>>>
>>> ** **
>>>
>>> at 25% this equation results in 0.2367, and my equation gets 0.1928****
>>>
>>> ** **
>>>
>>> Is there any other calculations going on in the background that is
>>> causing some problems?  I have attached an excel snapshot of the different
>>> EIR and the corrected EIR values for two different chillers in my program.
>>>  Neither is currently using the default EIR = f(PLR) curves, they are using
>>> custom curves.****
>>>
>>> ** **
>>>
>>> Thanks in advance,
>>>
>>> --
>>> Rob Hudson****
>>>
>>
>>
>>
>> --
>> Rob Hudson
>>
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>>
>
>
> --
> Carol Gardner PE
>
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