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Response to Mr. Bill powers comments
Letters to the Editor
683
Comments on "Theoretical and experimental studies on collector/storage type solar water heater" (Received 15 May 1983) Dear Sir, I write concerning the article "Theoretical and experimental studies on collector/storage type solar water heater", by Garg and Rani which appeared in Solar Energy' 29, 467-478 (1982). In stating in their conclusions "Use of insulation baffle plate improves the performance of the system significantly during day time as well as night time.", I wonder if the authors have taken into consideration the fact that the heaters equipped with the baffle plate contained less water than the other heaters? If not, the difference in day time performances could be accounted for by the water displaced by the insulating baffle, whose thickness (2.5 cm) is appreciable with respect to tank depth ( 10 cm). Some simple calculations lead me to believe that this is the case. Taking Fig. 9 I find that the temperature rise 7:01~15:00 hr for a heater without a baffle plate to be 32', tMember of the ISES.
with baffle plate (single cover glass), 42.5, a ratio of 0.753; but if the heater with the baffle plate contained 75% of the water (neglecting the vents in the baffle) in the heater without the baffle, there is no increase in performance. Again, in Fig. 12, until 12:00 hr the temperature rises (for heaters with single cover glass) are 24.3 ° for baffle thickness := 1.25 cm and 28.8 "~for thickness = 2.5 cm, a ratio of 0.845; the ratio of the volumes is 0.857 if no correction was made for the water displaced by the thicker baffle. It is ~orthwhile to clarify this point as night time performance can be improved by an insulated cover without the difficulties encountered in manufacturing a heater with a baffle plate, to say nothing of the health hazards presented by the presence of a thermoplastic in domestic hot water heaters.
lngenieur Solaire 07600 St- And~ol-de- Vals France
BILL POWErtst
Response to Mr. Bill Powers comments (Received 22 September 1983) Dear Sir, This is in pursuance to Mr. Bill Powers comments on my paper "Theoretical and experimental studies on collector/storage type solar water heater", Solar Energy 29, 467-478 (1982), which you have communicated to me vide your letter dated 18 May 1983. We have rightly concluded that the use of insulated baffle plate in the collector tank improves the performance of the system significantly during day time as well as night time in view of the fact that the system performance was studied with and without a baffle plate assuming different values of water
mass contained in the heater (m, = 25, 50, 100, 150, 200 kg) irrespective of the volume occupied by the baffle plate. This statement confirms that the system contained a constant mass of water (say 100 kg) and then its performance was studied with and without a baffle plate. Therefore, this clarifies the doubt of Mr. Bill Powers and hence all his other doubts stand invalid on this basis.
Indian Institute of Technology Hauz Khas New Delhi-110016 India
H. P. GARG
683
Comments on "Theoretical and experimental studies on collector/storage type solar water heater" (Received 15 May 1983) Dear Sir, I write concerning the article "Theoretical and experimental studies on collector/storage type solar water heater", by Garg and Rani which appeared in Solar Energy' 29, 467-478 (1982). In stating in their conclusions "Use of insulation baffle plate improves the performance of the system significantly during day time as well as night time.", I wonder if the authors have taken into consideration the fact that the heaters equipped with the baffle plate contained less water than the other heaters? If not, the difference in day time performances could be accounted for by the water displaced by the insulating baffle, whose thickness (2.5 cm) is appreciable with respect to tank depth ( 10 cm). Some simple calculations lead me to believe that this is the case. Taking Fig. 9 I find that the temperature rise 7:01~15:00 hr for a heater without a baffle plate to be 32', tMember of the ISES.
with baffle plate (single cover glass), 42.5, a ratio of 0.753; but if the heater with the baffle plate contained 75% of the water (neglecting the vents in the baffle) in the heater without the baffle, there is no increase in performance. Again, in Fig. 12, until 12:00 hr the temperature rises (for heaters with single cover glass) are 24.3 ° for baffle thickness := 1.25 cm and 28.8 "~for thickness = 2.5 cm, a ratio of 0.845; the ratio of the volumes is 0.857 if no correction was made for the water displaced by the thicker baffle. It is ~orthwhile to clarify this point as night time performance can be improved by an insulated cover without the difficulties encountered in manufacturing a heater with a baffle plate, to say nothing of the health hazards presented by the presence of a thermoplastic in domestic hot water heaters.
lngenieur Solaire 07600 St- And~ol-de- Vals France
BILL POWErtst
Response to Mr. Bill Powers comments (Received 22 September 1983) Dear Sir, This is in pursuance to Mr. Bill Powers comments on my paper "Theoretical and experimental studies on collector/storage type solar water heater", Solar Energy 29, 467-478 (1982), which you have communicated to me vide your letter dated 18 May 1983. We have rightly concluded that the use of insulated baffle plate in the collector tank improves the performance of the system significantly during day time as well as night time in view of the fact that the system performance was studied with and without a baffle plate assuming different values of water
mass contained in the heater (m, = 25, 50, 100, 150, 200 kg) irrespective of the volume occupied by the baffle plate. This statement confirms that the system contained a constant mass of water (say 100 kg) and then its performance was studied with and without a baffle plate. Therefore, this clarifies the doubt of Mr. Bill Powers and hence all his other doubts stand invalid on this basis.
Indian Institute of Technology Hauz Khas New Delhi-110016 India
H. P. GARG