Experimental investigations on small low flow SDHW systems based on mantle tanks

Side-by-side tests of two small SDHW systems based on mantle tanks have been carried out in a laboratory test facility. The systems are identical with exception of the vertical mantle tank. One of the tanks is the so-called Danlager 1000 marketed by Nilan A/S. The other tank is a test tank produced by METRO THERM A/S. Both tanks are built into 60 x 60 cm cabinets. In this way it is possible to bring the test tank on the market. Both hot water tanks have a total volume of 189 1 and an auxiliary volume of 86 1 at the top of the tank heated to 51 degrees C by a 1000 W electrical heating element during the tests. The hot water tank diameter is 492 mm and 400 mm for the Danlager 1000 tank, respectively the test tank. The height/diameter ratio for the hot water tank is 2.1 for the Danlager 1000 tank and 3.9 for the test tank. The mantle inlet for the Danlager 1000 tank is located at the very top of the mantle, while the mantle inlet for the test tank is located 125 mm from the top of the mantle. Both tanks are insulated with PUR foam insulation filling up the space between the tanks and the cabinets. Consequently the insulation thickness for the test tank is greater than the insulation thickness of Danlager 1000. The tests were carried out with the same daily hot water consumption of 100 1/day. Measurements of the thermal performance of the systems have been carried out for more than one year. The measurements show that the thermal performance of a SDHW system can be increased by about 15% by replacing the marketed tank with the test tank. It is thus documented that marketed mantle tanks can be strongly improved by increasing the height/diameter ratio, by increasing the thickness of the side insulation and by lowering the position of the mantle inlet.