How to Model Proposed and Baseline HVAC system for a District level heating and Cooling system

Not quite that simple. There are three options for how to model this. The first only accounts for the equipment inside the building and you treat the hot water and chilled water as purchased energy. In the other two you create a "virtual" plant in the model to simulate the effects of the DES including the losses, system efficeincies, etc. The Reference Guide contains specific guidance for how to model a District Energy System (DES).

Hi Marucs, I have a question about the first option, where only equipment inside the building is modeled. In my case, the building is connected to a district heating system solely for heating. This means I will model my proposed design with two loops: one representing the boiler (using a virtual DES) to simulate the district heating system with its respective supply temperatures, but I will set the default pump assigned by the software to zero consumption and non thermal distribution losses. In the other loop, which represents the downstream equipment, I will include the heat exchanger and the distribution pump (using the actual design's W/gpm) along with the design radiators. Then I will not consider any consumption for upstream equipment. I would appreciate if you can confirm if my assumption on how to model the proposed design is correct.

On the other hand, I am unsure about how to model the baseline system. According to the "Hot Water Pumps" section, it states that the baseline should have a primary loop only, and for a district heating system, a pump power of 14 W/gpm should be assigned. Does this mean I should model a single loop,as it would be without a DES, but with a pump rated at 14 W/gpm? Only that change? I am a bit confused by the section "G3.1.1.3.4 On-Site Distribution Pumps. All on-site distribution pumps shall be modeled in both the baseline and proposed designs." What does this mean for the baseline model? Should I have two loops? Should I model the baseline system with the actuall distribution pumps from the proposed design using the design's W/gpm and additionally the primary loop rated at 14 W/gpm?

Thank you for your clarification.

Your modeling description sounds like a combination of Path 1 and Path 2. For Path 1 you would not model any virtual DES plant, but instead you would simply model a purchased heating plant which represents the district heating system, connected to the building's downstream equipment as you described. 

The Baseline is modeled similarly, with a purchased heating plant connected to a building hot water loop with only the 14 W/gpm pump described. 

Hello,

We are working in a v4.1 Hospitality project which is served by DES for heating and cooling. We are building the model according to Path 1, but the language used in 90.1 - 2016 App G make us doubt about how to treat the Baseline System 2 for the residential spaces (our climate zone is 3A).

The statements in G3.1.1.1 and G31.1.2 remain very clear, but we do not understand why the section G3.1.1.3.3 does not make explicit mention to the System 2 in modification "b" (b. System 1 shall be constant-volume fan-coil units), as it is stated in G3.1.1.3.2 (b. System 1 and 2 shall be constant-volume fan-coil units with fossil fuel boilers).

In consistence with all the points mentioned above, we understand that, since we have purchased hot and chilled water, the System 2 PTHPs in the Baseline shall be constant-volume FCUs served by the purchased hot and chilled water plants, in the same way that we are modelling the proposed building served by the same purchased hot and chilled water plants, as designed.

Are we missing any point, or maybe there is a little lack of definition in G3.1.1.3.3?

Thank you

I'm guessing the reason is when both the heating and cooling are purchased energy, System 1 and System 2 become identical (constant-volume fan-coil units with chilled and hot water coils). 

That makes sense. Than you, Tyler.