Question

Water temperature in a storage tank is 40'C. DHW is used at 45°C. There are 4 mof solar collectors. Cold water is supplied at temperature of 10'C. There are no heat losses out of the storage tank. Water temperature in the tank cannot be lower than 10'C. a) In the first hour there is no useful energy supplied by solar collectors. In the first hour 40 liters of domestic hot water is used. Volume of a storage tank is 300 1. How much heat can be tracted out of the storage tank and how much must be provided by the auxiliary heater in the first hour? What is water temperature in the store after an hour? b) In the second hour there is 500 Whm of useful energy supplied by the solar collectors and 20 liters of domestic hot water is used. How much heat can be extracted out of the storage and how much must be provided by the auxiliary heater in the second hour? What is the storage temperature after an hour?

Answer 1

Auxilliary Heater outlet - t УУ loost Cold 450 Domestic Hot 400 water supply STORAGE TANK » Volume of tank = 300 Litre, Densfily of water = 1000 kg / water sulet Area of collector = 40 Specific heat of water = Klang 4.2 ks/ngr First hour since No useful energy is supplied by the Solar Collectors, so we can not extract any heat. A.) Water supplied = 40 lites. = 40 x103 m3 mass of water supplied - density & volume. = loo0 x 40 x103 = 40 kg Energy provided by auxilliary heater = m Cp AT = 40 x 4.2x (45-40) - 840 kJ Waten Tempt in storage after one hour. → (300-40) x 40 + 40 x 10 = 300xt - t = 36°c.

6 second howe Energy supplied by solar Collectoss = 500 wh/m2 Total energy supplied - 500 x 4 = 2000 W-hr. = 2000 x *JX 3600 s - 7200810 T = 7200 kJ mass of water used in second hour - Volumex density 20x10 3 x 1000 = 20 kg = → Energy provided by auxiliary heater = m C AT = 20 x 4.2 x (45-40) = 420 kJ → Energy used to increase the tempt of Cold water - in Cp PT = 20 x 402 x (40-10) - 2520 kJ Amount of Heat which can be extracted out of storage - Total Energy - Enesgy Consumed = 7200 - 2520 = 4680 kJ since there is sufficient amount of energy supply to storage tank so tempt of water in the tank after this hour is 40°6. →