[Equest-users] LEED DES Guidelines: Process Chilled Water and Steam

Sat May 27 10:04:39 PDT 2017

I have a very large and complex energy modeling project, and anyone who has tackled any of these issues and might offer some feedback would be appreciated.

The project includes a complex of manufacturing buildings that is pursuing LEED certification (BD+C version 2009).  Individual buildings are pursuing certification.  Cooling is provided by a central chilled water plant, which is part of the project and also one of the buildings seeking certification.  Heating is provided by a CHP that is on the complex but is not part of the project and being built and operated by the local utility company.  I have done several projects with district cooling and heating and know how to treat that using the LEED DES Guidance.

Complicating this, though, is that a significant portion of the energy use is process steam and process chilled water.  Process steam is from the same CHP.  Process chilled water is from a separate process chilled water loop, with the chilled water equipment housed in the same chilled water plant providing HVAC cooling.  The LEED DES Guidance does not explicitly state that the guidance applies to process loads, nor could I find any interpretations or guidance on how to treat process loads that are served by district energy plants.

Complicating the chilled water side is the fact that some of the process chilled water comes off the HVAC chilled water loop, and both the HVAC and process loop chillers utilize the same condenser water system, but I’m not even prepared to think about how to account for that yet.  For most of the buildings, I need to use LEED DES Option 1 anyway, which of course ignores the plants, because trying to eke out the minimum 10% energy savings for LEED will be the biggest challenge with the process load so high.

My initial thought was to put the process steam and process chilled water as constant loads on the energy model steam and chilled water meters, and applying the same rate as HVAC chilled water and steam as I am using based on the LEED DES guidelines.  The problem is the chilled water energy cost is higher using this method than accounting for the electrical use of the plant, and I am getting no savings from the improved efficiency of the process chilled water plant or the CHP.  My hope is to model the process chilled water system to demonstrate energy savings and also claim some steam energy savings from the CHP (hindering me is the fact that the CHP modeling is excluded from our scope of work so I don’t have a lot of information on it).

If anyone has any guidance based on experience with the following specific questions, I would appreciate it:

-Any known published guidance on treating process loads served by district thermal plants for LEED certification.

-Has anyone tried to model a process chilled water plant?  I have a huge thermal load cooled by the process chilled water system, but at the moment have no type of schedule or load profile so if I try to model the plant it will run at constant load 24/7.  I am also not sure how to place the thermal load into the buildings in eQuest.  I know how to add a natural gas thermal load, but not a steam load.  My thought was to add the process steam load as a natural gas load into a dummy zone in each building, set the natural gas utility rate to zero, set up a chilled water HVAC system served by my process chilled water loop to cool the dummy zone housing this load, and then set that HVAC unit fan energy use to zero to try and model the process chilled water consumption without adding electricity and gas consumption.  Any ideas on a better way to model this?

-The LEED DES Guidance Option 2 requires achieving 6 points minimum to use the option.  But there is an exception for buildings pursuing LEED that actually house the thermal plant.  My chiller plant building applies, however my chiller plant also receives steam from the CHP, which would seem to maybe negate the use of the exception.  Has anyone ever had this situation?

-As I mentioned modeling of the CHP is outside our scope, but it would help if I could claim some savings in process steam energy cost between baseline and proposed. If I can show enough savings in process steam, I might be able to hit the minimum 6 LEED points that allow me to use Option 2 and account for savings back at the plants, but I’m not sure how to claim this without modeling the CHP.  Has anyone claimed energy savings from a CHP that was not modeled?

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