ASHRAE 90.1 definition of ôFossil /Electric Hybridö

[DrRTU]

I cannot find an example of a “fossil/electric hybrid” system. When undertaking a 90.1-2004 appendix G simulation, we are required to select a baseline system from table G3.3.1a &b based upon a heating system. I have a building that I believe should be an Electric and Other system 6 (package VAV w/PFP boxes) but a USGBC reviewer has stated the baseline should be Fossil Fuel/Electric Hybrid, & Purchased Heat system 5 (package VAV w/reheat). The building is 80K sqft, 4 story office building with two 90 ton DX VAV package units with natural gas heat for morning warm-up. The building has series FP boxes with electric heat at perimeters and VAV boxes with reheat on the interiors. Use of natural gas accounts for 4.5% total BTUs of the heating load for the year and the balance being provided via electric heat terminals. Table G3.1.1A states “Where attributes make a building eligible for more than one baseline system type, use the predominant condition to determine the system type for the entire building” Has anyone had a similar LEED energy simulation issue and how was the baseline classified?

 

[RossABQ]

I would agree with your interpretation, but have no direct USGBC experience that corroborates it. If the gas usage is that small, is it worth using it (both from an initial cost perspective and a LEED perspective)? What are the costs of gas/electric in this case?

I did a quick search and found nothing explicitly defining a fossil/electric hydrid system, but it kind of sounds like a co-gen system?

 

[DrRTU]

I am glad someone else has the same opinion. I want to make sure I have a sound basis before proceeding.

Electric Rate = simple rate, straight consumption , no demand and no TOD. Rate = 0.111 $/KHh. Fuel gas = simple rate in therms @ 100.00 KBtu/Therm = 0.705 $/Therm. This is not a cogen system. The natural gas service only feeds the Two (2) 90 ton VAV package rooftops for morning warm-up. The building owner could have utilized electric MWU but now they are penalized because they purchased natural gas.

Thank you

 

[GMcD]

Welcome to the confusing, and open to interpretation rules of LEED, ASHRAE 90.1, and energy modeling being reviewed by third parties. I was an early adopter of LEED, getting my LEED AP in 2000, but after the last few years of the energy modeling rules and reviews, along with the credit reviews, I am convinced that this whole LEED thing has turned into a beaurocracy unto itself, and bears no reality to actually trying to save energy, or credit people with doing something more sustainable.

Dr. RTU - given your design system type I agree with the use of the System type 6 as being a realistic Baseline Building System. However, I have found that the reviewers are not necessarily as experienced as many of the practitioners out there, and really don't understand what the intent of, and what the Appendix G rules really mean.

When the ASHRAE 90.1 actually becomes a true energy standard instead of an economic energy standard, then maybe it will get simpler. Where I'm located, we get penalized for using electric heating over gas heating due to the fuel-switching rules, and the fact that the baseline building envelope rules for electrically heated buildings are different than the baseline envelope requirements for a gas heated building (Canadian EE4 energy modeling rules, and Model National Energy Code for Buildings)

We also have a local bun-fight going between our gas utility and the electrical utility - the electrical utility wants us to conserve electricity and reduce the use of electrically driven equipment and electric powered heating appliances (like heat pumps), while the gas utility wants us to reduce the use of gas-fired heating appliances and use more heat pumps. Nobody seems to be paying attention to basic building envelope design as the primary energy use conservation measure, so we get all glass condos with heat pumps as the flavour of the month, in a heating dominated climate with less than 100 degree days of cooling.....stupid.

 

[houseman20]

I agree with you that your baseline should model electric heat. You should argue that your design has gas preheat, and electric reheat. I wouldn't mention the building warm-up mode to the LEED reviewer, since that is not its primary heating method. You could always warm up with your electric reheat anyway.

According to Appendix G,
G3.1.2.3 Preheat Coils. If the HVAC system in the proposed
design has a preheat coil and a preheat coil can be modeled
in the baseline system, the baseline system shall be
modeled with a preheat coil controlled in the same manner as
the proposed design.