Effektivisering av pump- och fläktdrifter i byggnader. Elanvändning och systemlösningar.

Licentiate thesis, 2009

In this licentiate work the energy savings potential by more efficient pump and fan operation in buildings has been examined. The national savings potential in Sweden has been estimated based on available statistics and on information gained in a limited inventory. The estimated energy use for pump operation in residential and commercial (i.e. non-industrial) buildings in Sweden today is 2.2 TWh. If all pumps are replaced with the most efficient units available on the market today the savings potential is 1.5 TWh. The corresponding estimate of energy use for fan operation is 4.4 TWh. Replacement of all fans with the most energy efficient alternatives on the market would save 1.7 TWh. The development of electric motors and their control has led to small units being considerably better and cheaper. These small units can complement or replace traditional central units, which opens up for new system designs. Replacing the conventional large centralised unit with small decentralised units has been analysed theoretically and experimentally. For this purpose, two alternatives to the conventional temperature control of hydronic systems have been investigated. The alternatives are indirect flow control using valves and direct flow control using a pump. For ventilation applications, traditional VAV-systems are compared to a design that replaces the VAV-boxes with small decentralised fans. The focus in the analysis of the new system design is on the pressure drops that are introduced only for system control purposes. For decentralized designs, the largest energy savings appear at reduced capacity, i.e. at flows lower than the design flow. The savings potential is also dependent on the efficiency of the pump or fan. Efficiency measurements have been conducted on four pumps. Two of the pumps have maximum wire-to-water efficiencies exceeding 40 % and these high efficiencies are maintained over a wide operating range. The main factor to raise the efficiency is the use of permanent magnet motors. Measurements of the electricity use of a pump in a radiator system throughout a year were used as input for simulations of a radiator system. Two alternative flow control system designs were modelled; one system with flow control using a valve and one system with direct flow control using a pump. The results show that switching to direct flow control decreases the needed pump power to 5 % and the electric energy consumption to 0.5 % of the original values.