This case study involves a subsystem with several zones that are heated indirectly through a flat-plate heat exchanger. These zones are part of a greenhouse complex. The greenhouse subsystem had been in operation in this configuration for about a year, but there were numerous control and performance problems. This case study will describe the original configuration, performance problems, the solution, and the results. There are two appendices which cover some technical aspects in more detail.
The greenhouse is not heated year-round, so the zones are filled with Glycol. A heat exchanger separates the greenhouse zones from the rest of the heating system, which is filled with water.
The greenhouse is part of a much larger system that includes multiple heat sources and heat loads that are not part of this case study. It is important to note that the greenhouse and other heat loads are heated from a heat storage subsystem which consists of about 1000 gallons of hot water.