Both electric heat pump and district energy, what system?

Unless your building is 100% electric, your baseline system must be one of the odd numbered systems in ASHRAE Table G3.1.1.A. If you are purchasing ANY heat, you have purchased heat. So System 1 is the right choice.

I agree that system 1 is the correct choice since your system sounds like a fossil fuel/electric hybrid.

I don't necessarily agree with Chris' 100% electric statement in all cases. The note under Table 3.1.1A indicates that the predominant condition be used if more than one system type applies. Predominant in your case would likely be based on energy use and since your usage is close it would be hybrid and therefore system #1 but a different situation could be a system #2 with some fossil fuel heat.

A couple of other areas to evaluate - G3.1.1(a) outlines a possible exception which allows a secondary system to be modeled and also check out the DES Guidance on USGBC's web site to see if it may help your situation.

http://www.usgbc.org/ShowFile.aspx?DocumentID=7671

FYI - There is a new interpretation - posted 11/1/01 - which is helpful on this. Note that this supercedes some previous rulings - buildings which use gas for morning warmup only, now must be modeled against fossil fuel buildings

11/1/2011 ID# 10132

Ruling

Clarification is requested regarding when a building heat source in Table G3.1.1A should be identified as "Fossil/Electric Hybrid" versus "Electric".

The ASHRAE 90.1-2007 User's Manual states that a fossil/electric hybrid source "refers to a system with any combination of fossil and electric heat, and the baseline system for this is a fossil fuel system". Therefore, the heating source for the proposed building would be considered "Fossil Fuel" or "Fossil/Electric Hybrid" if the building uses any fossil fuel source for space heating (including backup heating or preheating), and the baseline building heat source would be fossil fuel.

Exception: ASHRAE 90.1 Section G3.1.1 Exception (a) stipulates additional system type(s) for non-predominant conditions (i.e. residential/non-residential or heating source) if those conditions apply to more than 20,000 square feet of conditioned floor area.

EXAMPLES OF BASELINE HEATING SOURCE DETERMINATION:

The Baseline heat source from Table G3.1.1A for the following Proposed Case system types would be fossil fuel since the proposed system design includes a combination of fossil and electric heat:

1. Variable air volume system with gas furnace preheat and electric reheat
2. Packaged terminal heat pumps with outside air tempered by fossil fuel furnace
3. Water source heat pumps with fossil fuel boiler
4. Ground source heat pumps with backup fossil fuel boiler
5. 90,000 square feet is conditioned by a variable air volume system with electric reheat, and 10,000 square feet is conditioned with fossil fuel furnaces

The following buildings would be modeled with an additional system type with a different Baseline heating source in accordance with Section G3.1.1 Exception (a):

1. 90,000 square feet is conditioned by a variable air volume system with electric reheat, and 20,000 square feet is conditioned with Packaged DX systems with fossil fuel furnaces. In this case, the 90,000 square feet of area would be modeled with an electric heat source in the Baseline Case (System Type #6 - Packaged VAV with Electric PFP Boxes), and the 20,000 square feet of area would be modeled with a fossil fuel heat source in the Baseline Case (System Type #3 - Packaged Single Zone AC with fossil fuel furnace).
2. 50,000 square feet is conditioned by water source heat pumps with a fossil fuel boiler, and 25,000 square feet is conditioned by electric heat pumps. In this case, the 50,000 square feet of area would be modeled with a fossil fuel heat source in the Baseline Case (System Type #5 - Packaged VAV with hot water reheat), and the 25,000 square feet of area would be modeled with an electric heat source in the Baseline Case (System Type #4 - Packaged Single Zone Heat Pump).

Good to know. Not going after the messanger here . . .

But this is not necessarily how I would interpret the word "predominant" in the note to G3.1.1A. With this interpretation a project could have 99% electric heating and 1% gas and be a hybrid system. So basically I'd be comparing electric heat to gas heat which is what 90.1 goes to great leangths to avoid. Using the term "any" seems to be a very extreme position in my opinion.