Heat Transfer Stations General Specifications 

General Requirements

Primary side pressure rating 10 bar

Secondary side pressure rating for new closed circuit system (with heat exchanger): according to BS EN 442

Minimum differential pressure on primary side: 0.4 bar. Differential pressure regulator required.

Design flow temperature, primary side: 95oC

Primary flow to modulate with flow demand of secondary circuit

Connection of heat exchanger to district heating pipes to be done by an approved plumber. Pipework to be adequately insulated and protected.

District heating valves to be easily accessible

SHEAP will supply the meter which has to be installed by an authorised person.

Copper in general should not be used on the supply to the heat exchanger unless approved by SHEAP prior to installation.

Galvanised steel pipes should not be used on District Heating systems.

High-pressure discharge valves must be piped to an external point close to ground level.

Note: The end of long lines may have a lower incoming temperature until more customers come on and this should be taken into account. In such cases SHEAP may require a temporary bypass to be installed sometimes with a temperature regulator. Properties between the incinerator and the boiler station have a primary side flow design temperature of 115oC.

New Radiator Circuit

The system must be a closed circuit and have inhibitor.

Design flow temperature to radiators: We prefer a maximum of 70oC but suggest that 55oC be considered.

Design return temperature from radiators: 35oC (closed circuits)

Heat exchanger capacity minimum 20kW, lower capacity to be approved of by SHEAP

Under-floor heating is very successful with district heating – check with suppliers for recommended floor temperatures.

Variable speed pump required

Bypasses should be avoided

Where plastic pipe is to be installed in closed heating circuits we recommend the use of barrier pipe

Existing Radiator Circuit

The return temperatures may be higher than for a new radiator circuit but will be accepted. However it is requested that any new radiators being installed are put to the requirements of the New Radiator circuit specification

Hot Water Circuit

It is recommended to avoid having a hot water storage tank unless there are likely to be exceptional heavy demands or there is a poor water supply.

Heat Exchanger Design

Heat exchanger capacity must be designed for maximum likely simultaneous demand according to the number of people and bathrooms in a building

Design flow temperature to heat exchanger: 85oC (although in practice it will be nearer 95C in the winter).

Design hot water temperature: 50oC at a minimum flow rate of 0.3 litres/sec for a three bedroom house. Large households to be designed accordingly

Control (Optional)

Self acting or electronic

Possible time clock for radiator system

Radiators highly recommended to be equipped with thermostatic regulating valves.

Large users should have a drive open/spring drive closed valve on the primary side.

Groups of Domestic Units (ie Flats)

Please refer plans to SHEAP for approval

Lerwick District Heating Scheme Regulations

1. All connections to the Lerwick District Heating Scheme must be made in accordance with these regulations.

2. All works on the primary side of the District Heating scheme installations must be undertaken by a company employing plumbers approved by Shetland Heat Energy and Power Ltd. (SHEAP) Similarly, all works on the secondary heating side not using a heat exchanger must also be undertaken by approved plumbers.

3. The District Heating network will operate at a maximum temperature of 95oC (except on the line from the Energy Recovery Plant to the Peak Load Boiler Station which will normally be 110 - 115oC) and be designed for a pressure of 10 bar.  A differential pressure of a maximum of 0.4 bar will be maintained between the distribution pipes..

4 Heat Transfer Stations (Heat Exchangers)

This must be approved by SHEAP.

The primary side should be sized for 40oc - 95o for a new heating system with a maximum pressure loss of 0.15 bar.  Older systems can be permitted to operate at their current temperature regimes, but any future modification should be undertaken to lower  the return temperature.

All pipe connections for the district heating network to the heat exchanger must be made of steel pipes in accordance with DIN 2440, 2441, 2448/1629 or 2458/626.  The primary pipes must be kept accessible and the isolation valves kept clear.

All pipework from the termination points to the heat exchanger should be insulated.

5 The Meter

The meter will be supplied by SHEAP. The approved plumber will be required to install the meter with consideration that the meter might need to be replaced. The meter will be required to be connected to the mains electricity supply. The meter supplied will have a system that transmits readings via radio.

6 Pressure Test

SHEAP may require a pressure test taken on the primary side to a pressure of 15 bar.

7 Sizing of Heating Systems

The customer should ensure that a new radiator system has been designed to achieve the required cooling of the water.

For low temperature radiators the following guide is recommended :


8 Operating Connections

Prior to opening the main shut-off valves, the plumber should notify SHEAP.

9 Draining of District Heating Water

The District Heating water is purified and treated with chemicals and must only be drained after agreement with SHEAP. Adding of untreated water on the primary side must not take place.

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