Overview of a Smart Energy Combined Cooling, Heating, and Power System at a Hospital
Overview of a Smart Energy Combined Cooling, Heating, and Power System at a Hospital
Overview of a Smart Energy Combined Cooling, Heating, and Power System at a Hospital
1. System Overview
A smart energy system centered on a building-level combined cooling, heating, and power (CCHP) system was adopted for a newly constructed 18-story hospital building with a floor area of 25,000 m². The projected energy demand of the building was as follows:
- Electricity: peak load of 2,200 kW
- Heating: winter daytime heating load of about 3,000 kW (equivalent to 4.5 t/h of 0.6 MPa saturated steam), and nighttime load of 2,200 kW (3.3 t/h). In addition, domestic hot water required 2.5 t/h of steam during the day and 1.5 t/h at night.
- Cooling: summer daytime cooling load of 4,300 kW (equivalent to 6.5 t/h of 0.6 MPa saturated steam), and nighttime load of 3,200 kW (4 t/h). Hot water demand was basically the same as in winter.
Due to policy restrictions, coal was not allowed as a power fuel. In addition, the hospital’s heat-to-power ratio exceeded 2:1 in both winter and summer. Therefore, this project adopted a gas-turbine-based CCHP system.
According to the feasibility study report, if a gas turbine were used together with a waste heat boiler, steam absorption chiller, and steam-water heat exchanger, while oil-fired boilers supplemented the system whenever the thermal load exceeded the output of the waste heat boiler, the overall energy conversion efficiency could reach 71% (assuming all equipment operated at design load during both the cooling and heating seasons).
2. Project Implementation and Operation
The system was equipped with a 1,000 kW gas turbine cogeneration unit to provide cooling, heating, power, and domestic hot water for the hospital building. The installation consisted of one gas turbine generator set, one single-drum serpentine forced-circulation waste heat boiler, two oil-fired boilers, two lithium bromide absorption chillers (each with a cooling capacity of 1,000,000 cal/h; 1 cal = 4.1840 J), and other auxiliary systems. The total project investment was approximately RMB 15 million.
2.1 Performance
Under design conditions, the unit generated 1,130 kW of electricity and supplied 3.3 t/h of 0.8 MPa saturated steam. When using light diesel oil as fuel, the overall efficiency reached 71%, representing a 20% energy saving compared with separate supply.
2.2 Economic Analysis
The actual economic performance of a CCHP unit is closely related to changes in real operating loads. The key question is under what load conditions operation remains economically advantageous. At the initial stage of the project, fuel oil was priced at about RMB 2,200 per ton, but that price has since more than doubled. Calculations showed that only when the oil price remained below RMB 2,200 per ton could its fuel cost be comparable to natural gas priced at RMB 1.9/m³. As a result, fluctuations in diesel prices caused this project to lose its economic viability only a few years after commissioning. This serves as an important cautionary lesson.
Conclusion
Gas-turbine-based cogeneration systems offer clear technical advantages in buildings: they require less building space, have a high degree of automation, involve relatively low maintenance workloads, and deliver high-quality power generation. However, fluctuations in energy prices are a major reason why such projects may fail. Therefore, for any proposed CCHP system, in addition to technical feasibility, trends and volatility in energy prices are often critical factors that determine the success or failure of the project.
