1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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%

9. 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

10. 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
126 2
80.000 86 … N
220
Total:
1.152
SS #
Area [m2]
Heat capacity share [%] 1
11,0% 2
80.000
7,5% … N
19,1%
Total:
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

11. 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.

12. 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

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