District heating, district cooling, and also heat rejection

[hrydberg]

Hi,

I have two questions that I'd be happy to find answers to.

First, in ApSys, how do I model a system which is heated by district heating and cooled by district cooling, in terms of seasonal efficiency, delivery efficiency, and SCoP for the heating part and seasonal EER, delivery efficiency and SSEER for the cooling?

For district heating I would like to put all the values above to 1, but choosing district heating in the UK NCM wizard gives me other values, with a delivery efficiency lower than 1. Is this to cover for heat losses in the system? There is no district cooling option in the UK NCM wizard. Here I want to choose the same approach and have a delivery efficiency of 1, or perhaps 0.95 to cover for cooling losses. Am I correct in doing so?


The second issue, which fuzzes me even more - the option "Heat rejection: Pump & fan power (% of rejected heat)". This is by default set to 10 %. By testing different values in simulation, I can see that a higher percentage results in lower chiller energy use, but instead an increased energy use for heat rejection fans and pumps. What is this? When would it be used?

Thanks!