Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 1| 1 Utilization of return water in district heating networks Oddgeir Gudmundsson Application Specialist Marek Brand Application Specialist Jan Eric Thorsen Director Danfoss District Heating Application Centre DK-Nordborg

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 2| 2 Content Introduction Concept Technology Cases Conclusion

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 3| 3 Introduction For district heating to maintain economic feasibility in the worlds energy structure it is important to allow the concept to develop A clear development can be seen when considering how the network temperature levels has changed from the 1 st generation towards the 4 th generation district heating systems This development has increased the network efficiency through reduced heat losses and also opened up for variety of new heat sources At the same time the distribution pipes and the pipe insulation has been developed in effort to further reduce the distribution heat losses and to simply the process of constructing the distribution network Similarly the control equipment and heat exchanger units have been developed to optimize the system operation This development has occurred for the last 30 years, however majority the building stock is still the same or may have been lightly renovated through that time New and renovated buildings generally have lower temperature level requirements. This fact has opened up for cascading usage of the energy supplied through the district heating network

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 4| 4 1G 2G 3G 4G Introduction

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 5| 5 Concept District heating schemes are operating with various temperature levels depending on the original design of the network and the connected building stock In many cases existing buildings may require high supply temperatures and consequently have high return temperatures, f.ex. supply of °C and return of 40-60°C Sufficient temperature levels vary and depend on the heating installations New energy efficient buildings with floor heating installation only need supply temperatures of 35-40°C to fulfill their heating requirement Domestic hot water (DHW) temperature of 45°C is considered sufficient for everyday use. Having DH supply temperature of 50°C is sufficient for preparing DHW at 45°C via instantaneous heat exchanger solution, without risk of Legionella. This fact gives the opportunity to utilize the return flow from existing areas in new areas and hence utilize the capacity of existing DH networks to a greater extend with minimum investment costs. Utilize further the capacity of the distribution network Increased efficiency at the plant due to lower return temperature Reduced heat losses in the return line

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 6| 6 Conceptual example of cascading energy usage in district heating All energy classes Newly constructed / renovated areas multi-apartment single-family Recently build and renovated Non-renovated older buildings CHP waste incineration CHP natural gas Large scale solar Low-energy buildings High temperature supply, 90°C High temperature return, 50°C Low temperature return, 25°C

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 7| 7 Utilization of return water for existing buildings Renovation of the existing network  Low Temperature District Heating

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 8| 8 Low Temperature DH for existing buildings  Project supported by the Danish government  75 single-family buildings from 1997  Floor heating Realisation  New low-temperature DH in-house substation  New DH network  Heat loss reduced from 41% -> 14%  80% of heat demand supplied from main DH return line  Before transition average T supply = 70-75°C  After transition average T supply = 55°C

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 9| 9 Area substation As the DH return temperature can vary it may become necessary to raise the return temperature before it is supplied to the secondary network This can be achieved by mixing the return water with hot water from the main DH supply pipeline Primary network T supply =90°C T return =52°C T return =26°C Sønderby Area substation Sønderby low temperature DH T supply =52°C Sønderby Last consumer Substation at the consumer Thermostatic bypass

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 10

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 11 Micro booster – Reduced temperature levels  Ultra-Low Temperature District Heating

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 12 Objective: Maximum utilization of district heating return flow Ultra-Low Temperature DH for existing buildings  Project supported by the Danish government  4 single-family buildings from before 1960  Radiators, mix of 1 pipe and 2 pipe systems Realization  Micro heat pump DH substation in each house to boost the supply temperature for instantaneous preparation of Domestic Hot Water  New U-LTDH network  Heat loss only 46% of the heat loss that would be experienced in a traditionally designed network  Area heat exchanger substation connected to the main district heating network regulates the supply temperature  Supply temperature kept as low as possible at all times Area substation

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 13 For floor heating temperature levels of 30-40°C are sufficient Domestic hot water of 45°C is sufficient for all normal use With instantaneous preparation of DHW there is no risk of Legionella Micro heat pump unit boost the supply temperature to 53-55°C and stores the water in a primary side located storage tank until DHW tapping occurs Condenser Evaporator Instantaneous DHW preparation No Legionella risk DH side storage tank Micro booster concept Micro booster installed

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 14 Heat exchanger area substation The aim of the substation is to maintain constant secondary side temperature of 40°C As the DH return temperature can vary primary side supply is mixed with the return to maintain constant 45°C supply to the heat exchanger by means of a pump control

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 15 Pump Pressure gauge m. afsp. og studs Temperatur sensor Thermometer One-way valve, check valve Energy meter Control valve Shut-off valve, NL normally closed M FE Frequency control Heat exchanger Expansion vessel s Controller

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 16 How applicable can this be?

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 17 Low-temperature DH for existing buildings  Supported by the Danish government  8 single-family houses from 1970  With traditional radiators: 70/40/20°C  How much could T supply be reduced without sacrificing comfort? Numerical simulations  Many possibilities  Various refurbishment stages  Low-temperature radiators 70°C 40°C heat output 100 % 50°C 33°C heat output 55 % same radiators ṁ = constant

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 18 Duration of T sup over/equal certain temperature Heating curves for radiators  Single-family-house from 1970 – results from simulation ! Low-temperature substation for DHW T supply [°C] hours above certain temperature [%/a] *Extensive renovation = low energy windows + roof insulation =

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 19  Existing buildings can be supplied with LTDH already today if T supply is in cold periods increased above 50°C  Required T supply to radiators depends on:  desired indoor temperature  state of the building  heating system  DH companies should be more strict in reducing T supply to:  reduce heat losses from DH network  integrate more renewables  DHW applicatoin should always be changed to low- temperature one LTDH for Existing Buildings

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 20 Conclusions There is a potential to further utilize the capacity of existing district heating network and reduce the network return temperature significantly by cascading the energy use Studies show that with light renovation of buildings the requirements to the DH supply temperature sinks significantly As new areas are built or building areas renovated close to existing district heating network it is possible to establish district heating network with low investment costs utilizing the remaining heat in the return pipeline from the existing DH grid

Nordic Show Room on Energy Quality Management, th August 2014, O. GUDMUNDSSON, DANFOSS A/S | 21 Thank you for the attention Contact information: Oddgeir Gudmundsson Application Specialist, Application Centre Danfoss District Energy, DK-Nordborg