We're working on a small project (7,500 SF) pursuing LEED NC v2009 designed with water-source VRFs served by a shared central condenser water system with cooling towers, boilers, and pumping. The CW system is located entirely off-site (outside the LEED project boundary) and serves multiple buildings within a LEED Campus boundary. CIR #5234 provides some guidance on the issue, but not enough for a clear understanding of how to handle this particular system. The definition of a DES within the LEED DES Guidelines doesn't directly apply to CW systems, but we're still unclear on how to appropriately account for this system and what approach to take. Question #1: Do we have to follow the LEED DES Guidelines? If so, how do we handle the Baseline system (would be System #3). Question #2: Are we allowed to segment the central plant capacity - meaning since I know the percentage of the central plant attributed to this building can I model an on-site plant configured like the central plant but with reduced capacities, flows, etc?
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Haojie Wang
Energy ModelerKJWW Engineering
4 thumbs up
March 30, 2016 - 2:46 pm
Are you reading DES v2? They have two options. Options 1 is to use virtual utility rate and model the central plant cost-neutral in proposed and baseline. But in your case, I think option 2 is better suited for you since you have more efficient cooling plant. And your central plant is just cooling tower, you can just model it as on-site plant, which is described in detail in DES v2.
Jake Torok
April 5, 2016 - 9:57 am
Thanks for your response. I think the issue here is that condenser water systems are not directly covered in DES v2 and technically the primary space heating/cooling is being performed on site with the plant serving more as a heat sink. This entire system (cooling tower, boilers, pumps) is located offsite with this building only accounting for ~10% of the total load on the plant. If I pursue Option 2, then part-load operation becomes a concern because this building accounts for such a small percentage of the total capacity. My previous questions was "Are we allowed to segment the central plant capacity - meaning since I know the percentage of the central plant attributed to this building can I model an on-site plant configured like the central plant but with reduced capacities, flows, etc?"
Jake Torok
April 5, 2016 - 9:59 am
Thanks for your response. I think the issue here is that condenser water systems are not directly covered in DES v2 and technically the primary space heating/cooling is being performed on site with the plant serving more as a heat sink. This entire system (cooling tower, boilers, pumps) is located offsite with this building only accounting for ~10% of the total load on the plant. If I pursue Option 2, then part-load operation becomes a concern because this building accounts for such a small percentage of the total capacity. My previous questions was "Are we allowed to segment the central plant capacity - meaning since I know the percentage of the central plant attributed to this building can I model an on-site plant configured like the central plant but with reduced capacities, flows, etc?"
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5916 thumbs up
April 25, 2016 - 12:39 pm
You are not required to use the DESv2 but if you don't you will need to justify your own modeling protocol for the situation.
Even though the system you have is not directly addressed you can apply the same principle in the DESv2 to your situation.
Under Option 2 you model a virtual central plant that is on-site and sized to your project. See section 2.4.1.2.