Page 234 - Low Temperature Energy Systems with Applications of Renewable Energy

Heating with geothermal systems 221

4. In view of the different climate conditions in Iceland and The Netherlands, write a short
essay contrasting the basic design considerations for greenhouses in these two place with
emphasis on the most influential factors in each case.
5. Describe the advantages and disadvantages of shell-and-tube versus plate-type heat ex-
changers, specifically for geothermal greenhouse duty.
6. Section 5.5.2 describes an aquaculture facility in Iceland, an island country with a large fish-
ing industry. List and briefly describe as many other similar countries as you can where
geothermal-assisted aquaculture is being done or have the potential to do so.
7. Explain why one would use two-stage refrigerators and heat pumps? Give the reasons for
the transition from one-stage to a two-stage compression?
8. Show on the T-s diagram an ideal two-stage cycle and the areas that represent the reduction
of work and increase of cooling capacity compared to a one-stage cycle.
9. Why are different working fluids used in the lower and upper cycles of a cascade unit?
10. Compare cascade and two-stage refrigerators. Show which machine has the higher theoret-
ical cooling coefficient of performance COP.
11. How does the installation of the additional equipment listed below influence the cooling
COP of the cycle: (i) subcooler, (ii) regenerative heat exchanger, and (iii) economizer?
12. What is the reason for using an economizer in the two-stage heat pump system in Fig. 5.36?
13. Compare the thermodynamic efficiency of a cycle with two-stage compression and incom-
plete intermediate cooling with a single-stage cycle.
14. How can the operating mode of a refrigeration system with partial intercooling be trans-
formed to full intercooling operation mode (RHE circuit)?
15. Show the flow diagram and thermodynamic T-s diagram of a two-stage refrigeration ma-
chine with full intercooling and with parallel throttling.
16. Repeat Question 15 except for a cycle with full intercooling and successive throttling.

Exercises

1. With reference to the data in Table 5.3, estimate the thermal supply capacity (in MWth) of the
City of Boise, Idaho, using a mass-weighted geofluid supply temperature for the three pro-
duction wells and the stated reinjection temperature. You may assume a specific heat of
4.19 kJ/kg K for the geofluid.
2. Estimate the average thermal supply capacity (in MWth) of the U.S. Veteran’s Administra-
tion geothermal heating system for the period 1997e2002 assuming a reinjection tempera-

ture of 45 C. You may assume a specific heat of 4.19 kJ/kg K for the geofluid.

Acknowledgments

One of the authors (RDP) thanks the following individuals for answering questions and
providing additional information, data, and materials regarding their geothermal projects: Del
Eytchison, Manager, Boise Warm Springs Water District, Boise, Idaho; Jon Gunnerson,
Geothermal Coordinator, Public Works, City of Boise, Idaho; Ric Johnston, Facilities Manager,
Division of Public Works, State of Idaho, Boise, Idaho; and Radboud Vorage, Project Director,
Greenhouse Geo Power, IJsselmuiden, Netherlands.