Pumparbete samt returtemperatur för tre alternativa lösningar vid koppling till luftvärmare
Examensarbete för masterexamen
In buildings, pumps and fans are major users of electric energy. There are pumps and fans in air-handling units. The task of the air handling unit is to provide the desired thermal indoor climate according to the demand of the users of the building. Buildings need heating or cooling in order to achieve the thermal comfort level. To do this we need to transfer a desired amount of heat to or from the air which passes through an air handling unit. This will be done normally by using hot or cold water in a system which transfers the desired amount of heat between water and air in an air handling unit. This system regulates traditionally with valves and valves give rise to pressure drop. The pressure needed in water systems is produced by pumps and the pressure needed in air systems by fans. To run fans and pumps requires electric energy. To save energy we need to run the system with minimal pressure drop. Each single reduction in the total energy use is meaningful. In this work the focus will be on pumps. This investigation has targeted water-to-air coils for heating but the principles apply also to cooling coils. Three alternatives have been studied: traditional systems with temperature control (so called “shunting”), flow control with two-way valves and di-rect flow control with variable speed pumps. In a temperature controlled system, the desired transferred heat is controlled by mixing return water, which has a low tempera-ture, with hot water from a heating source. In flow control with a two-way valve, the desired transferred heat is controlled by a valve which decreases or increases the flow. In flow control with a variable speed pump the desired transferred heat is directly con-trolled by the pump with no assistance of valves. The results show that “shunting” causes the largest pressure drop and thus largest use of electricity. Flow control with a two-way valves introduces a pressure drop that is slightly less than “shunting” and thus the use of electricity is also slightly less. Direct flow control with a capacity controlled pump results in the smallest pressure drop and thus also the lowest use of electricity. By comparing the ratio of heat power divided with the use of electricity for these systems, it is possible to decide which one is most efficient.
Byggnadsteknik , Building engineering