Värmeåtervinning ur spillvatten i befintliga flerbostadshus
Drain water heat recovery is an uncommon measure in multi-unit residential buildings. There istechnology available for the purpose but the knowing and experience of the heat recovery systems islittle. The purpose of this thesis is to evaluate the future potential of drain water heat recovery inmulti-unit residential buildings.A major part of the multi-unit residential buildings in Sweden were built during modernismen andrekordåren (1940?1975). Many of the buildings have worn out drain and water supply systems andmany are in need of a general refurbishment. If drain water heat recovery is considered for a buildingit is suitable to install the recovery system at the same time as the refurbishment to minimize theinstallation cost.Existing heat recovery systems consist of heat exchangers, heat pumps or a combination of both.There are passive heat exchangers that are placed close to the shower, on the vertical drain pipe andon the horizontal drain pipe. Recovery systems comprising heat pumps are more complicated andspace demanding. They are rarely suited for multi-unit residential buildings but have the potential ofrecovering more heat from the drain water.In some buildings, where heat recovery systems have been installed, the performance of the systemshas been measured. The measurements show that passive heat exchangers can recover about 10?15 % of the hot water energy consumption, not including standstill losses and hot water circulation.Calculations indicate that the energy savings for passive heat exchangers could be 20-25 %. If severalkinds of heat exchangers are combined the energy savings could be almost 40 %. Recovery systemswith heat pumps could generate even larger energy savings, between 50?70 %. However, with heatpumps the electricity consumption increases and that has to be considered in profitabilitycalculations. When developing new heat recovery systems the emphasis should be on energy storageand reactivity since most taps are short and unpredictable.In a technology procurement there should be demands on energy effectiveness. Based on experiencefrom installed heat recovery systems and calculations the following is suggested:?The buildings heating and hot water energy consumption must decrease with at least 15 % ofthe current hot water energy consumption.?The buildings heating and hot water energy consumption should decrease with at least 20 %of the current hot water energy consumption.Furthermore there should be demands on profitability. The present value of future energy savingsought to exceed the investment cost and the present value of future costs of the system within aperiod of time. The following is suggested:?The condition must be fulfilled within 20 years?The condition should be fulfilled within 15 yearsiii