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Meter Advice & Guidance

Energy meter types.

Energy meters generally fall in to two categories, heat energy and cooling energy. There are also meter versions capable of measuring both heating and cooling energy.

Heat energy is typically low temperature hot water coming in to a property or area from a heat source and returning cooler. Cooling energy is where the flow or inlet medium is colder than the returning temperature back to the supply source.

An energy meter comprises of three parts, the inline flow meter fitted in to the pipework, a pair of temperature sensors (one for the flow pipe and one for the return) and an energy calculator.

Never cut or extend temperature sensor cabling. Never cut or extend the signal cable between the flow meter and the calculator.

How does an energy meter work?

Energy meters measure the energy required to provide the heating, hot water or cooling in thermal energy units eg. Kilowatt Hours KWh or Megawatt Hours MWh.

An energy meter is a device which measures thermal energy on the supply side or return side of a heat generating, heat exchanging device, or cooling source by measuring the flow rate of the heat / cooling transfer fluid and the change in its temperature (delta temperature ΔT) between the supply and return legs of the system.

The energy is calculated based on the flow rate of the water or water / glycol mix and the difference in temperature of the flow and return medium.

Terminology.

Flow / Inlet pipe - The pipe from the source of heat or cooling entering an area.
Return / Outlet pipe - The pipe from the area returning to the energy source.

All manufacturers program their meters at the factory to be installed on the return pipe unless otherwise advised i.e. the colder pipe for heating networks and warmer pipe for cooling networks. Many meters now allow the end user to select the installation position prior to fitting the meter. It is important the installation position is selected correctly otherwise a meter may be up to 10% inaccurate and more importantly will fail an application for the RHI schemes.

On a heat network, if the meter is programmed for the flow / inlet pipe, be careful with temperature sensor installation location. For example the hot (red) temperature sensor may need to be inserted in to the meter body to replace the cold one that may have been installed at factory.

In addition on cooling networks, follow the manufacturers instructions carefully, for example, on some brands the red (hot) temperature sensor actually is installed on the flow / inlet pipe which is the colder pipe.

How to size an energy meter.

Meters are sized on two parameters, the pipe size they are being fitted to and the flow rate. Often the flow rate is unknown. Each meter has a qp value, also known as the nominal flow value. At this flow rate, the meter is its most accurate. Importantly, it is not recommended for the flow to go over the qp rating of the meter for any prolonged period (20 minutes in a 24 hour period) due to cavitation and pressure loss issues. It should be noted that all meters will measure up to twice their qp rating, this is called the qs value. For example a meter with qp 2.5 m3/hr will measure up to qs 5.0 m3/hr. The minimum flow (qi) of a meter will be stated on the data sheet which is typically 100 times less than the qp so the meters also measure very low flows for the respective pipe size.

Meter connections / terminology.

Threaded or screwed meters typically range from 1/2" BSP up to 1 1/2" BSP in size. Flanges are used for sizes DN50 (2") up to DN400 (16"). Some manufacturers offer flanged meters for small sizes such as DN32 or DN40 where required. Flanges are either PN16 or PN25 rated depending on meter manufacturer.

Meter descriptions are typically based on the union size or flange size. For example a DN20 or 3/4" meter has 1" BSP connections on the flow meter body and 3/4" BSP male threads on the unions that are normally supplied with the meter.

Refer to the following for general guidelines of the meter size to use with your pipe size:-

15mm pipe - use 1/2" BSP Meter
22mm pipe - use 3/4" BSP meter
28mm pipe - use 1" BSP meter
32mm pipe - use either 1" BSP qp 6 meter or 1 1/4" BSP meter
35mm - use either 1 1/4" or 1 1/2" BSP meter
40mm - use 1 1/2" BSP meter
54mm - use DN50 meter

Larger pipe sizes tend to be more inline with the meter size, for example, use DN65 meter on 65mm pipe and so on.

Meter technology.

Most of the meters offered by Stockshed are ultrasonic time of flight technology where there are no moving parts and extremely accurate. In addition Stockshed offer the Sontex range of meters which work on a fluid oscillation principle, also providing highly accurate metering.

MID Approval and RHI (Renewable Heat Incentive).

All meters offered by Stockshed are Class 2 MID approved to EN1434 making them suitable for tenant billing applications and the RHI schemes.

IMPORTANT: Be aware there are a few UK metering companies offering mechanical water meters with a pulse output coupled with heat or cooling energy calculators connected to a pair of temperature sensors. Whilst in theory this creates a low cost heat or cooling energy meter, and the individual components may be MID approved, the system as a whole is not MID approved and is not acceptable to Ofgem (the governing meter regulator) for billing or RHI schemes.

Also note that "clamp on" meters, which do not require cutting in to the pipe work, are not MID approved and therefore can only be used for reference measurement and not billing or part of an RHI scheme.

Glycol applications.

On some applications, Glycol is mixed with water or a preblend Glycol is used to provide antifreeze protection. On these applications it is important to note that all ultrasonic meters do not work properly when Glycol is present. There is only one brand of meter approved for use with Glycol that Stockshed offer. These meters are programmed and documented accordingly with the type of Glycol in the system and the % concentration used for Ofgem approval. The relevant documentation is provided with the meter on delivery.

The above information is for guideline use only, if you require specific advice or assistance please contact us.