Understanding how heat and cooling energy meters work, how they are sized and how they should be installed is essential when selecting the correct meter for an application.
This guide explains the basic principles of thermal energy metering, including meter types, terminology, sizing, connections, installation position, metering technology and glycol applications.
Energy Meter Types
Heat, cooling and combined heat/cooling energy measurement.
Energy meters generally fall into two main categories: heat energy meters and cooling energy meters. There are also meter versions capable of measuring both heating and cooling energy.
In a heating system, heated water typically enters a property or area from the heat source and returns at a lower temperature. In a cooling system, the flow or inlet medium is colder than the returning medium.
A complete energy meter typically consists of three principal components: an inline flow meter installed in the pipework, a pair of temperature sensors — one for the flow pipe and one for the return pipe — and an energy calculator.
Important: Never cut or extend temperature sensor cabling. Never cut or extend the signal cable between the flow meter and the energy calculator.
How Does an Energy Meter Work?
Measuring flow and temperature difference to calculate thermal energy consumption.
Energy meters measure the thermal energy used to provide heating, hot water or cooling. Energy is normally displayed in units such as kilowatt-hours (kWh) or megawatt-hours (MWh).
The meter measures the flow rate of the heat-transfer or cooling medium together with the temperature difference between the flow and return sides of the system. This temperature difference is commonly referred to as Delta T (ΔT).
The energy calculator uses the measured flow rate and temperature difference, together with the characteristics of the heat-transfer medium, to calculate the amount of thermal energy transferred.
Energy Meter Terminology
Understanding flow, return and meter installation position.
Flow / Inlet Pipe: The pipe carrying the heating or cooling medium from the energy source into the area being served.
Return / Outlet Pipe: The pipe carrying the medium from the area being served back towards the energy source.
Energy meters are commonly factory-programmed for installation in a particular pipe position, often the return pipe unless otherwise specified. Many modern meters allow the required installation position to be selected before commissioning.
It is important that the programmed installation position corresponds with the actual position of the flow meter. The temperature sensors must also be installed in the correct flow and return positions.
Check Sensor Position Carefully
On a heating network, if the meter is programmed for installation in the flow/inlet pipe, the temperature sensor arrangement may need to be changed. For example, the hot (red) temperature sensor may need to be installed in the meter body in place of the factory-installed cold sensor.
Cooling applications require particular care. Sensor conventions and installation arrangements can vary between manufacturers, so always follow the installation instructions supplied with the specific meter.
How to Size an Energy Meter
Correct meter selection should consider both pipe size and actual system flow rate.
Energy meters are primarily selected according to two parameters: the pipe size and the flow rate through the system. Pipe size alone should not be used to determine the correct meter.
Each meter has a qp value, also referred to as its nominal or permanent flow rate. This is an important figure when selecting a meter for the expected operating conditions.
Understanding qi, qp and qs
qi – Minimum Flow: The lower flow-rate limit specified for the meter.
qp – Permanent / Nominal Flow: The flow rate around which the meter is normally selected for continuous operation.
qs – Maximum Flow: The meter's specified upper flow-rate limit. For example, where qp is 2.5 m³/h, qs may be 5.0 m³/h depending on the particular meter.
Continuous operation above the meter's qp rating should be avoided unless specifically permitted by the manufacturer. Excessive flow can increase pressure loss and may adversely affect the installation.
Always refer to the individual manufacturer's data sheet for the meter's qi, qp and qs values and allowable operating conditions.
Meter Connections & Sizing Terminology
Threaded, union and flanged connections for different pipe sizes and flow requirements.
Threaded or screwed energy meters typically cover smaller pipe sizes, while larger meters normally use flanged connections. Flanged meters are commonly available from DN50 upwards, although some manufacturers also offer smaller DN32 and DN40 flanged models.
Flange pressure ratings are commonly PN16 or PN25 depending on the meter manufacturer, size and model.
Threaded meter descriptions can sometimes cause confusion because the meter body connection and the pipe-side union connection are different sizes. For example, a DN20 / 3/4" meter may have 1" BSP connections on the flow meter body with unions reducing the connection to 3/4" BSP male threads.
General Pipe Size Guide
- 15mm pipe: 1/2" BSP meter
- 22mm pipe: 3/4" BSP meter
- 28mm pipe: 1" BSP meter
- 32mm pipe: 1" BSP qp 6 or 1 1/4" BSP meter
- 35mm pipe: 1 1/4" or 1 1/2" BSP meter
- 40mm pipe: 1 1/2" BSP meter
- 54mm pipe: DN50 meter
Larger pipe sizes tend to correspond more directly with the nominal meter size — for example, a DN65 meter on a 65mm pipe. These are general guidelines only; the actual system flow rate should always be considered when selecting the meter.
Energy Meter Technology
Ultrasonic and static measurement technologies with no conventional mechanical measuring mechanism.
Many of the energy meters supplied by Stockshed Metering use ultrasonic time-of-flight technology. These meters have no moving mechanical measuring parts and provide highly accurate flow measurement across a wide operating range.
Stockshed Metering also supplies the Sontex Superstatic range, which uses a static fluid-oscillation measuring principle and provides an alternative highly accurate solution for thermal energy measurement.
MID Approval & RHI Applications
Selecting appropriately approved equipment for billing and regulated metering applications.
When an energy meter is required for tenant billing or a regulated metering application, it is important to select a complete metering system carrying the appropriate approval for its intended use.
Heat meters are commonly manufactured and approved in accordance with EN 1434, with Class 2 meters widely used for commercial thermal energy measurement.
Check the Complete Metering System
A mechanical water meter with a pulse output connected to a separate energy calculator and temperature sensors should not automatically be assumed to constitute an approved heat-meter system simply because the individual components carry separate approvals.
Always check the approval status of the complete energy-meter configuration for the intended billing or scheme application.
Clamp-on meters: Clamp-on ultrasonic meters can be extremely useful for temporary measurement, system analysis and reference monitoring. However, their suitability for regulated billing or scheme applications should be checked against the applicable approval requirements.
Glycol Applications
Special consideration is required where glycol is present in the heat-transfer medium.
Some heating and cooling applications use glycol mixed with water, or a pre-blended glycol solution, to provide frost and freeze protection.
The presence and concentration of glycol changes the physical properties of the heat-transfer medium and must therefore be considered when selecting and configuring an energy meter.
Stockshed Metering supplies specialist meters suitable for glycol applications. Where required, these meters are programmed according to the glycol type and concentration used within the system.
Glycol applications: Glycol programming must be completed prior to meter dispatch. Please contact us before ordering so we can confirm your application requirements and ensure the meter is programmed correctly.
Need Help Selecting an Energy Meter?
Selecting the correct heat or cooling meter depends on pipe size, flow rate, operating temperature, installation position, heat-transfer medium and communication requirements.
The information above is intended as a general guide. If you require assistance selecting or sizing a meter for a specific application, please contact Stockshed Metering and we will be happy to help.