Hydraulic balancing in district heating systems operated according to PUSH philosophy Oddgeir Gudmundsson, Jan Eric Thorsen and Marek Brand Danfoss Heating Segment Application and Technology

Content Definition of PUSH and PULL systems Differences between PUSH and PULL systems Example of flow and heat balance Out of phase syndrome in PUSH system Balancing with a new innovative balancing method Conclusions

Definitions of PUSH and PULL systems The consumer is in control of the heat supply and draws off the heat he requires to fulfill his heating demands Applied control equipment: Automatic controls PUSH systems: The heat supply is based on planned heat production in respect to outdoor air temperature Applied control equipment: Manual balancing valves TRV + ASV RLV MSV-F2 MSV-F2

Differences between PUSH and PULL systems PUSH systems : Billing is fixed, typically according to heated square meters The heat supply is centrally determined The heat is supplied to the buildings independent on if they need the heat or not Target: minimum indoor temperature level Not comfort driven In general area substations are applied and there is a lack of controls in the buildings Flow in the distribution network is generally manually controlled Hydraulic balance is difficult to achieve PULL systems : Billing is based on actual heat consumption Heat meters are used to determine the heat consumption Heat supply is consumer driven The indoor temperature is set by the consumer Maximizing comfort Domestic hot water preparation via DH Individual and automatic controls are the norm Flow in the distribution network is controlled automatically Hydraulic balancing is simple

Typical PUSH systems Only manual controls Substation operation profile: - Manual balancing - Constant flow on primary and secondary side Area substation Area substation Area substation Heat plant Area substation DH operation profile: - Constant head from pump - Constant flow - Weather compensation at heat plant Area substation

Example of flow balance and hydraulic balance - Design Primary side: Plant output = 120 ton/hr at 90°C supply and 50°C return Each substation is designed for 20 ton/hr (930 kW) at 40°C cooling of the supply HEX is designed for 2°C dT between secondary inlet and primary outlet Secondary side As in real systems the operation of the secondary side varies Different return temperatures are experienced Manual balancing is iterative and in principle newer ending ! Unknown heat loss Distribution loss Water loss 120 t/h 30 t/h 10 40 20 20 t/h 48°C 53°C 58°C 43°C 46°C 55°C 930kW 814kW 698kW 1047kW 978kW 768kW

Hydraulic balance within the day - Out of phase syndrome The supply temperature needs to be adapted to the demand This is a huge issue in constant flow / manual balanced systems! Larger the network the more problematic it becomes Flow time in a large DH Case: Average forecasted temperature 6 hours in advance at the plant location Supply temperature is then kept fixed for 6 hours

Hydraulic balance within the day - Out of phase syndrome Time Targeted heat supply is +/-10% of the demand. How well do they perform? Substation 1: 63.8% of the time within +/-10% Substation 2: 44.1% of the time within +/-10% Substation 3: 27.0% of the time within +/-10% Substation 4: 19.1% of the time within +/-10% Substation 5: 18.1% of the time within +/-10% Substation 6: 22.3% of the time within +/-10% Rest of the time there is either over or undersupply situation! During oversupply periods heat will be lost due to “open window regulating” During undersupply periods tenants will complain To avoid complaints the plant operator will increase the supply temperature All additional heat supplied will be a loss to the DH company! Can easily lead to 30% oversupply  Heat loss! Average: 32.4%

Our solution We have developed a new balancing solution focusing on PUSH based district heating systems The new solution is simple to operate and is based on the planned heat production principles How it works: The operator defines the capacity split between the connected substations First function: Fair split of the flow Second function: Fair split of the plant capacity Third function: Weather compensation at substation level The new solution will automatically adjust the valves positions in the substations according to the specified profile No need to continuously making manual balancing If adjustments are required the operator can at anytime easily redistribute the flow/heat through the solution interface

Basic user inputs - First and second function The operator provides the following information for each substation First function (fair split of the flow): Maximum allowable flow volume of each of the connected substations Second function (capacity limitation): Maximum allowable share of the plant heat capacity SS # Area [m2] Max flow [m3/h] (dTdesign=40°C) 1 100.000 126 2 80.000 86 … N 120.000 220 Total: 800.000 1.152 SS # Area [m2] Heat capacity share [%] 1 100.000 11,0% 2 80.000 7,5% … N 120.000 19,1% Total: 800.000 100% Peak demand [MW] Each substation is then allowed: To draw off its maximum defined heat capacity… As long as it using less then its maximum defined flow rate

Basic user inputs - Third function - Builds on the first function inputs Third function (capacity limitation): Heating demand curve of each of the connected areas: Each substation is then allowed: To draw off its maximum defined heat capacity as specified by the heating index curve… As long as it using less then its maximum defined flow rate The difference from the 2nd function is that the 3rd function is reacting to the instant demand at the substation while the 2nd function is reacting according to the heat plant output.

Conclusions The new solution can significantly reduce oversupply situation in PUSH systems by intelligently control the heat delivery by still operating according to the PUSH principle Initial commissioning of the system will become significantly faster and simpler Any later flow adjustments can be made with controlled impact on consumers downstream

Thank you for your attention Contact information: Jan Eric Thorsen or Oddgeir Gudmundsson Director, Projects Danfoss Heating Segment, DK-Nordborg og@danfoss.com