Optimization of a DH System by Maximizing Building System Temperature Differences
Summary of the final report of the project
An effective district heating (DH) system has two primary distinguishing features: a low supply temperature and a high temperature difference between the supply and return ?DT). A low supply temperature results in an increased overall efficiency if combined heat and power (CHP) and/or waste heat is utilized, while a high DT results in low flow in the DH system.
In this study, the principle of cascading loads in building heating systems was used to increase the temperature difference between the supply and return. To thoroughly evaluate the thermodynamic and economic performance of different building systems, all three main DH components (heat production plant, distribution network and building heating system) were considered as an integrated system. In order to identify the optimum design of each of the building heating systems, a series of case studies, based on notional groups of buildings, were performed and comparative thermodynamic and economic analyses produced.
These case studies comprised combinations of:
- four building types: large multi-functional building (sport facility), single-family
homes, multi-family home blocks and small office buildings;
- several district heating substation configurations with cascading space
heating loads and/or domestic hot water loads for each building type;
- two climates, Amsterdam and Toronto, for single-family homes, multi-family
home blocks and small office buildings; a third climate, Sudbury (Ontario,
Canada), for large
- multi-functional buildings; and a combined cycle gas turbine CHP plant with
natural gas-fired peaking boilers as a heat production source.
Computer models for the entire DH systems were developed using Simulink software and the heating systems were simulated for an entire year. The results are presented in a series of graphs and tables for each case analyzed. The graphs and tables show the DH temperature differences (flow weighted DT), DH water flow, the DH system operation costs as well as revenue generation.
The results showed that for all cases examined, the DH DT increased by cascading of the heating loads. However, the magnitude of the improvement in DT varied for the different types of buildings.
For the large multi-functional building, there were eight thermal loads requiring different supply temperature levels. This building provided greater opportunities for maximizing DT than were present in the other building types.
The eight loads (at the design outdoor temperature of -30°C) were:
1) Pool ventilation air handler - Air Handler 3
2) Fin-tube convectors for perimeter heating
3) Three ventilation air handlers - Air Handler 1
4) Glycol-based floor heating above parking garage
5) Fan-coil heaters (shut off at nighttime)
6) Floor heating in daycare
7) Pool water heater (constant)
CANMET Energy Technology Centre, Ottawa, Canada
NUON Technisch Bedrijf, Duiven, the Netherlands
JFR Engineering I/S, Denmark
Gagest Developments Ltd, Canada