Page 212 - Low Temperature Energy Systems with Applications of Renewable Energy

Heating with geothermal systems 199

Fig. 5.23 Piping in the hot water plant at Cuckoo Polder [25].

greenhouses via a double-pipe system wherein the hot water feeds each greenhouse off
the supply line and the cooled water is collected in the return line. The hottest water is

used to grow cucumbers and plum tomatoes. The water is reduced to about 37 C after
these greenhouses, and is further used for low-temperature growing of organic seeds

and strawberries. By then the water temperature has dropped to essentially 20 C
where it is returned to the collector line, mixing with the water at 32 C being dis-

charged from the first two greenhouses, and arrives at the heat exchanger for reheating.
Some of the piping in the hot water plant is shown in Fig. 5.23.
There are three plate-and-frame (P&F) heat exchangers in the hot water plant. P&F
units are particularly appropriate for this application owing to their flexible design and
tolerance of impure geofluids. Fig. 5.24 is a schematic of a P&F heat exchanger showing
how the hot fluid and the cold fluid pass on opposite sides of corrugated, thin plates. Gas-
ketsprevent mixingofthefluidsandkeepthemintheirproperchannels.Theunitsarevery

Fig. 5.24 Plate-and-frame heat exchangers as used in Cuckoo Polder greenhouses, after [22].