The UK’s approach to heat metering is farcical

Sontay, RHI, heat metering, BMS, BEMS, controls
Responsibility for proper heat metering — Alan Braybrook.

Metering heat has a vital role to play in the UK’s long-term energy strategy, But Alan Braybrook of Sontay is concerned and frustrated at what is happening in the field.

The European Union has set targets for reducing carbon emissions of 20% by 2020 and 80% by 2050. However, change may be on the way. The coalition is keen for the EU to increase the 2020 target to 30%. The agreement of other EU countries to such an increase in the targets would benefit Europe’s long-term low-carbon aim. Increasing the targets now means we are more likely to reach the 80% target in 2050.

Commercial buildings currently generate around 20% of the UK’s total carbon emissions. With new targets on the agenda it is now more important than ever for the building-services sector to minimise fuel consumption and cut energy costs.

But how do we actually prove that we are delivering on these objectives? Accurate and reliable metering is surely the answer. If only it were so simple.

Heat metering in the UK is an area typified by inadequate specification, poor installation techniques and a lack of knowledge — which completely compromises the performance of the meter itself.

Let me explain why.

First, let us take a look at the legislation. The 2010 Building Regulations require reasonable provision for the installation of energy meters in buildings with a floor area greater than 1000 m2 and which enable at least 90% of the fuel to be assigned to the various end-use categories (heating, lighting etc.). Following ‘CIBSE Guidance TM39: Building energy metering’ is advised to ensure best practice.

Meanwhile, the European Commission’s Measuring Instruments Directive (MID) is also important. Approval to MID is required for meters used in any billing application, including heat and water meters. Instruments have to meet the general essential requirements of the directive plus one of 10 instrument-specific annexes. With the MID European Type Approval Certificate, an instrument may be freely sold and used in any European country. MID and the harmonised standard EN 1434 (which is widely used to prove compliance) deals not only with meter compliance but also with the requirements for installation and maintenance.

So far, so good. The problems are in the detail of what actually happens on site.

Problem one is that the wrong meter is often used for an application.

Broadly speaking, there are two types of products — flow parts for water (water meters) and flow parts for heating (flow sensors). It is the latter which should be used for heat metering, not the former. Far too frequently, this is just not the case. Too many building-services engineers simply select and install meters on lowest cost alone and not on whether the meters themselves are actually correct for the application.

Metering heat and billing for it requires sophisticated and approved equipment.

Heat meters comprise three parts: a flow sensor to measure volumetric flow; a pair of matched temperature sensors; and a calculator. Many engineers are confused about flow meters designed for non-continuous flow (such as water meters) and those designed for continuous flow.

Water meters designed for non-continuous flow typically have an upper temperature limit of 90°C and are generally limited to flows not exceeding three hours per day over a 6-year period. Flow sensors for heat-meter applications typically have an upper temperature limit of +130°C and are designed for continuous flow — 24 hours a day, every day. Water meters used in heat-metering applications (i.e. high duty or continuous flow) are unlikely to retain the accuracy over the normal 5-year lifespan of the product and should not therefore be specified or installed.

Using a water meter designed for non-continuous use paired with a MID approved heat-meter integrator will render any installation inaccurate and irrelevant.

An MID-approved integrator must be connected to a flow sensor to ensure accurate measurement and billing. MID product approval is determined by the international metrology institute, the PTB (Physikalisch-Technische Bundesanstalt — Any changes made to the integrator must be carried out at a PTB-approved laboratory. Changes are carried out in the field such as reprogramming of an integrator will mean that the integrator is no longer accurate and will not meet the MID compliance requirement, so it cannot be used for billing purposes.

Metering is not a one-size-fits-all kind of business. Far from it. Contractors and consultants have a responsibility to ensure their clients have compliant meters fitted for the right application, since the use of unapproved meters for billing carries a potential risk of prosecution. An industry source I came across recently claimed that 90% of meters currently fitted in commercial buildings are not compliant for billing purposes. Our own experience at Sontay makes me fear that this figure, unlike the numbers recorded by the vast majority of UK metering installations, is, regrettably, an accurate one.

There needs to be a vast improvement in specifying, selection and commissioning of heat-metering applications to ensure that the correct information is being derived from these meters and, more importantly, that the building occupiers are being billed correctly.

Who is going to take responsibility? 

Alan Braybrook is sales and marketing director with Sontay.

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