Case Studies
ITC- IRC, Bangalore
Indian Institute of Science, Bangalore
Forbes-Gokak Mills, Gokak
Wells Fargo

Indian Institute of Science (IISc.)

Client: Indian Institute of Science (IISc.)
Location: Bangalore.
Year: 2009
PROJECT: Trouble shooting and revamping of solar water heating system at the new mens’ hostel.

Background:

IISc is a world renowned education institute offering courses in science and engineering at graduation, masters and doctorate level courses and research fellowships.The newly constructed gents’ hostel with ground plus 5 floors had 885 rooms. The hostel was equipped with sophisticated solar water heating systems of 7,500 LPD(Liters per day)X 2 nos. supplied by one of the leading manufacturer to cater to the needs of bathing for the inmates. The system had a heat exchanger wherein the primary water being circulated in the solar collectors was heating the secondary water stored in the huge stainless steel tanks. Water thus heated was supplied to the bathrooms through long distribution network of pipes. Soon after installation they started facing complaints from the inmates that the water is not sufficiently hot or it would take a long time before hot water reached the taps, especially in the lower floors. The management tried to address the problem by various means of calling the supplier and asking him to rectify the defects. It was observed that there used to be repeated failures of the thermostatically controlled circulation pumps. Several experts had studied and many changes were carried out. However all these measures were found to be short lived and inadequate as the problem persisted. In the meanwhile the protests and anger from the student community was reaching peaks.

OBSERVATIONS:

IISc entrusted the task of studying and suggesting necessary changes to solve the problem.A detailed study was carried out to identify the problems and the following lacuna were short listed:

  • The centralized storage solar water tank was observed to be quite far from the usage points in the various floors. Hot water had to travel almost 70 meters on the roof before reaching the service chute which took the pipes down to the floors. Being a 5 storeyed building water had to traverse further before reaching the taps. This resulted in long delay in hot water reaching the taps as a large quantity of cold water had to be drained before getting hot water. The problem was aggravated due to irregular usage of the hostel mates and long intervals between consequent baths, hence the wastage was repeated.

  • The system was equipped with heat exchanger and primary and secondary sides of water were separated. This resulted in drop in temperatures due to heat exchanger efficiency. Such systems are recommended when the water has high content of minerals(hard water of more than 200 p.p.m. TDS(Total dissolved solids). It was noted that the hostels were getting treated water from the Bangalore Water supply, the water of which was below 200 ppm. Hence it was concluded that the specifications were unnecessarily over designed.

  • The 7,500 liters tanks were also equipped with …..kW electric heaters which needed to be switched on when heating from solar was not sufficient like on cloudy days. It used to take a very long time to heat up such a large quantity of water and did not meet the requirements.

  • The bathing pattern was throughout the day at irregular timings, with many students taking baths in the morning, some in the late afternoons and many in the nights.

  • The system was provided with a thermostatically controlled circulation pump for circulating primary water during the day. The control cables were laid on the roof of the hostel and running into long distances. Although the control cables were laid in PVC conduits, the same was getting damaged by rats and squirrels. It had become a nightmare for the maintenance staff to keep reconnecting the broken cables. Even the circulating pump motor could not be run due to frequent power cuts. Without sufficient circulation of water, no heating was taking up.

  • Due to long disuse, many solar collectors were found to be in poor state, some of the glasses were broken, leakages inside the collectors had rusted the boxes etc.

Recommendations

  • It was recommended that the centralized single huge storage tank of 7,500 Liters tank should be discarded and in its place to go in for de-centralised smaller systems .

  • The location of these systems were recommended to be just above the service shafts which reach out to bathrooms within a short distance instead from a long distance.

  • Since the bathing pattern was irregular, the hot water was getting mixed up with cold make up water whenever water was drawn. This was solved with installing two separate system in series. It was decided to put 1,500 liters systems two numbers in series, each system having its own 12 collectors. Hot water from the first tank was made into make up water for the second tank. This ensured there was no mixing of cold make up water in the supply tank. Thus students taking baths at different times would get hot water at any time of the day or night.

  • The forced circulation was eliminated in these smaller systems since the thermosyphon effect was sufficient to cause circulation of water from collectors to storage tanks and back.

  • Heat exchanger model was discarded in the new system and there was direct heating, thus eliminating the inherent temperature drops in heat exchangers. There was no need for separation of primary and secondary waters since water quality(total hardness) was within the limits.

  • Several collectors were repaired and additional new collectors were recommended to take care of decentralized system.

  • In addition, it was recommended to fix a small 25 liters capacity electrically heated geyser in each bathrooms. This would switch on automatically if the incoming water temperature was less than 600 C. This eliminated the centralized electric heaters of high wattages which were fixed on the 7,500 Liter capacity tanks.

RESULT

IISc went through a tendering process based on all the above recommendations. After due delligence a contractor was selected. Part of the contractor’s responsibility was also to take back the old tanks, pipes, collectors etc. which became redundant. IISc were extremely happy with the performance of the refurbished system.