Dear Friends,
I have a project located at Dubai where a localized existing district cooling plant will be providing chilled water. However the DCP supplier is not willing to share any information about their information with us. In this case I guess I need to go with energy model for Option 1 ( Building stand-alone scenario). It is stated that the energy source of both baseline and proposed buildings will be purchased chilled water. And it is quite clear that baseline water-side setting will follow ASHRAE 90.1 Appendix G (in my case the baseline chiller COP will be 6.1 etc.).
My question is: shall I use the same water-side setting (proposed chiller COP of 6.1 etc.)for proposed building as well?
Or shall I use the default chiller plant efficiency of 4.4 for proposed building?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
March 21, 2017 - 10:27 am
Option 1 is purchased energy. So there is no chiller in either model. You should use 90.1-2007 Addendum ai which addresses chilled water systems more explicitly.
Mark JIN
March 21, 2017 - 10:25 pm
Dear Mr Sheffer,
Thanks for your reply. I understand that option 1 is purchased energy. If no chiller in either model, what cooling source should i use in the energy model (Im using IES VE)? Is there any document addressing details of how to set up purchased energy or purchased chilled water in energy model?
Rgds,
Mark
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
March 22, 2017 - 8:46 am
Not sure exactly how to do it in IES-VE but in general there should be an option within the creation of the plant to select purchased chilled water. I am not aware of a generic document but I would think that the IES-VE manuals or the help desk should be able to address the subject. There is also a discussion group for IES-VE at onebuilding.org
Cory Duggin
Senior Energy WizardTLC Engineering Solutions
53 thumbs up
March 22, 2017 - 10:31 am
For purchased chilled water in the VE, you need a CHW loop with a water-cooled chiller. Then set the chiller curve to be Virtual DES Chiller and set the COP=1.This gives the water cooled chiller curve coefficients that make the curve flat. Finally, make the cooling tower fan power 0. You will have to post process the CHW cost because until VE2017 there is no way to create a separate energy meter. I have also used the COP as a conversion factor between the electricity rate and the CHW rate, so the program calculates cost correctly, but then the energy savings is off.
Mark JIN
March 23, 2017 - 12:28 am
Hi Cory,
Thanks for your guidance. Could you tell why COP of purchased chilled water shall be equal to 1? Just curious on that since the energy consumption will be super high with such a poor COP.
Rgds,
Mark
Mark JIN
March 23, 2017 - 5:32 am
Hi Marcus,
It is stated that only downstream saving should be included for district cooling Option 1.
Shall I include purchased chilled water cost when calculating overall project energy cost saving?
Thanks,
Mark
Cory Duggin
Senior Energy WizardTLC Engineering Solutions
53 thumbs up
March 23, 2017 - 9:57 am
Setting the COP=1, basically turns the cooling energy into kBtu of CHW. It will make the energy look high, but getting the energy cost accurate is the focus.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
March 23, 2017 - 11:28 am
If you follow 90.1-2007 addendum ai you just use the rate from the district system. If you follow DES v2 Option 1 use the guidance in the DES v2 Section 2.4.2.1.
Mark JIN
March 24, 2017 - 12:10 am
Hi Marcus,
Thanks for the guidance.
I follow DES v2 Option 1. Please have a look at the paragraph (extreme bottom) copied describing virtual DES rate. Got several questions still.
1. Im a bit confused on that 'Flat rate'. Is there any reference for this flat rate?
2. I understand that virtual rate of district chilled water is derived from virtual electric rate. But how can I know the virtual electric rate then?
3. Will the virtual electric rate be applied to all building equipment such as lighting, receptacle consumption?
Separate virtual DES rates are calculated for each type of energy supplied by the DES (e.g., chilled water, hot water, or steam) based on the virtual energy rates for each type of fuel. If a flat rate structure is being used for all energy sources (meaning the cost per unit energy is the same throughout the year, and there are no demand charges), then these flat rates simply become the virtual energy rates for the project.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
March 24, 2017 - 9:48 am
1. A flat rate is expressed as $/unit of energy that does not change. A national average rate is an example of a flat rate.
2. The virtual rate is derived by the energy model. It is the rate determined by the end result of the modeling expressed in $/unit. The virtual rate and flat rate are the same if a flat rate is used. If a more complex rate structure is used in the model the rate is not flat and the model determines the virtual rate. For example suppose you enter a rate with a customer charge, a tiered set of charges for kWh depending on usage, and a demand charge. The virtual rate is the simple, flat rate that results from the modeling result. So you need to do a modeling run to determine the virtual rate if you are not using a flat rate.
3. The rate used for other equipment should be determined based on Appendix G. You can use a flat rate (determined in many possible ways) or use the actual rate tariff from the utility serving the project.