6.3 Building services - heating system efficiency
Functional standard
6.3.0 Introduction
6.3.1 Methods of demonstrating efficiency
6.3.2 Heating systems with higher carbon intensities
6.3.3 Space heating controls
6.3.4 Hot water service system controls

standard 6.3
mandatory

In order to comply with standard 6.1 every building must be designed and constructed in such a way that the heating and hot water service systems are designed, installed, and capable of being controlled to achieve optimum energy efficiency having regard to the thermal transfer of the insulation envelope.

Limitation

This standard does not apply to:

1. buildings which do not use fuel or power for controlling the temperature of the internal environment;
2. buildings, or parts of a building which will not be heated, other than heating provided for the purpose of frost protection;
3. heating systems for frost protection;
4. individual, solid-fuel stoves or open-fires, gas or electric fires or room heaters (excluding electric storage and panel heaters) provided in domestic buildings.

6.3.0 Introduction

The heating system of a building should be designed and installed to make efficient use of energy for the conservation of fuel and power. Where this is not possible the U-value of the insulation envelope should be improved (see 6.3.2 below).

Conversions

In the case of conversions, as defined by Regulation 3, the building as converted must be improved to as close to the full requirements of this standard as is reasonably practicable, and in no case be worse than before the conversion (Regulation 12, Schedule 6).

6.3.1 Methods of demonstrating efficiency [J11.1]

In the case of liquid or gaseous-fuelled boilers, one way of demonstrating this would be to achieve compliance with the Boiler Efficiency Regulations 1993 and 1994.

For all types of boilers or other primary heat sources, a way of demonstrating this would be to ensure the rating-weighted average carbon intensity of the boiler or other primary heat source is in accordance with Table 1, below:

Table 1: Maximum carbon intensities of heating systems

Carbon intensity of heating plant

Notes :

1.The carbon intensity of the heating plant is based on the carbon emitted per useful kWh of heat output and applies to boilers, heat pump systems and electrical heating, and is given by:

A = B ÷ C (Equation 1)

where:

1. is the carbon intensity of the heating system (kgC/kWh of useful heat); and
2. is the carbon emission factor of the fuel (kgC/kWh of delivered fuel) obtained from Table 2; and
3. is the gross thermal efficiency of the heating system (kWh of heat divided by kWh of delivered fuel).

Table 2: Carbon emission factors

Combined heat and power (CHP)

2. Where a combined heat and power system (CHP) is proposed, the carbon intensity of the CHP can take account of the benefit of the on-site generation in reducing emissions from power stations feeding the national grid by using the following equation;

A = (B ÷ D) — (F ÷ E) (Equation 2)

Where:

1. is the carbon intensity of the heating system (kgC/kWh of useful heat);
2. is the carbon emission factor of the fuel (kgC/kWh of delivered fuel) obtained from Table 2 to this specification;
3. is the heat output ratio of the CHP engine (kWh of heat per kWh of delivered fuel);
4. is the electrical output ratio of the engine (kWh of electricity per kWh of delivered fuel);
5. is the carbon emission factor for grid supplied electricity (kgC/kWh). This should be taken as the factor for new generating capacity that might otherwise be built if the CHP had not been provided, i.e. the intensity of a new generation gas-fired station at 0.123 kg/kWh
6. This adjusted carbon intensity can then be used in equation 1 to determine the carbon intensity of the overall heating system at 100% and 30% of heating system output.

CHP heat dumping

3. Where the CHP has no facility for heat dumping, the gross thermal efficiency is the CHP heat output divided by the energy content of the fuel burned. Where the CHP includes facilities for heat dumping, the gross thermal efficiency should be based on an estimate of the useful heat supplied to the building, i.e. the heat output from the CHP minus the heat dumped.

If the carbon intensity of the system is too high, the guidance in 6.3.2 should be followed or the Carbon Emissions Calculation Method adopted for the whole building.

6.3.2 Heating systems with higher carbon intensities

There may be certain cases where the use of a heating system with a high carbon intensity is unavoidable, for example, grid-supplied electric direct-acting panel heaters. In such circumstances it is appropriate for the U-values of the insulation envelope to be improved to offset the potential increase in carbon emissions. The improved U-values are determined by dividing the individual U-values (in Table 1 to 6.2.1) by 1.15 and rounding down the revised figure to 2 decimal places.

The guidance can then be considered to be followed if:

1. These U-values are adopted as the maximum for the proposed building, when using the Elemental Method (6.2.1); or

These U-values are adopted for the ‘design’ of the notional building, when using the Heat Loss Method (6.2.2) or the Carbon Emissions Calculation Method (6.2.3).

Frost and condensation protection

6.3.3 Space heating controls   [J11.2] [J11.3] [J11.4]

Good control of space heating is essential for conservation of energy in buildings, as without it, the potential of energy-efficient heating plant cannot be realised. Generally the system should have sufficient zone, time and temperature controls to ensure that the heating system only provides the desired temperature when the building is occupied. Such operating controls can be overridden however, when heating is needed to protect the building’s structure, services or contents from frost or condensation damage.

Room temperature control

Where rooms or other areas are designed to have different temperatures during the hours of occupation, the space heating system should incorporate either thermostatic radiator valves (TRVs) or room thermostats/sensors.

Time controls

Where the space heating is to be intermittent and does not make use of off-peak electricity, the system should only operate when the building is normally occupied or is about to be occupied:

• Systems with an output of more than 50kW should have optimum start and stop controls. These ensure that the building or zone reaches its occupation temperature at the appropriate time but can override the time control during mild weather and comfort is not compromised by energy efficiency.
• Systems with an output of not greater than 50kW should have manually adjustable automatic 7 day programmers or timers that can be set to suit the occupation of the building or zone.

Weather compensation for wet systems

A weather compensation function should be installed in a wet heating system, which is linked to an outside sensor. This will automatically reduce the boiler flow temperature, in line with an increase in the external temperature.

Electric storage Heaters

Electric storage heaters should incorporate an automatic charge control which is linked to a sensor. The sensor will adjust the electrical charge to the appliance according to the room or zone temperature. When room temperature is high the charge is reduced and visa-versa. Heat output control should be given to the building occupant by incorporating a damper or fan in the heater.

Boiler inhibit controls

Solid fuel boilers

Boilers generally

Boiler inhibit controls should be installed to prevent the gas or oil-fired boilers operating when there is no demand for heat, but a pump overrun may also have to be fitted as required by the manufacturers. In the case of a solid fuel boiler, it should be thermostatically controlled to reduce the burning rate of the fuel. For safety reasons a slumber circuit for such boilers should be formed. Generally for all boilers a bypass circuit should be fitted if the boiler manufacturer requires one or specifies a minimum flow rate whilst the boiler is firing. An automatic bypass valve should be used where the system comprises a substantial number of TRVs.

Sequence control for boilers/CHP

If the system comprises two or more gas or oil-fired boilers, a sequence control should be installed to match the number of boilers operating to the heating demand for the building. As this minimises the number of boilers firing, it also avoids short-cycling of burner operation and overall energy efficiency is improved.

• If there is a mixture of condensing and ordinary boilers installed, the condensing boiler should operate first.
• If combined heat and power (CHP) is installed in conjunction with the boilers, the CHP should be the lead heat source.

www.actionenergy.org.uk

Good Practice Guide 132 published by Action Energy gives examples of appropriate controls for wet heating systems and their use in non-domestic buildings. An appropriate system of space heating controls is one that is designed to the above guidance and also follows the advice in GPG 132.

Boilers (not solid fuel)

6.3.4 Hot water service system controls [J11.5]

A hot water service system should have controls that will switch off the heat when the water temperature required by the occupants has been achieved and during periods when there is no demand for hot water.

If the system does not incorporate a solid fuel boiler, consideration should be given to the following:

• the heat exchanger in the storage vessel should have sufficient heating capacity for effective control, such as one manufactured in accordance with BS 1566: Part 1: 2002 or Part 2: 1984 (1990) or BS 3198: 1981. In particular it should follow the recommendations in these standards for the surface area of heat exchangers (i.e. pipe diameter and number of coils).
• a thermostat should be fitted which switches off the heat when the storage temperature required by the occupants has been achieved. In the case of combined space heating and hot water systems this thermostat should be interconnected with the other controls which are needed to form the boiler inhibit.

a manually adjustable 7-day automatic timing device should be installed to control the periods of operation. This can be either as a part of the combined space heating and hot water system or as an independent device.

Solid fuel boilers

With a solid-fuel fired system however, where the cylinder is not forming the slumber circuit, a thermostatically controlled valve should be installed

Instantaneous water heaters

Where an instantaneous water heater is installed which is local to the point of use, no additional controls are needed other than those supplied with the appliance.

www.actionenergy.org.uk

Good Practice Guide 132 published by Action Energy gives additional advice and examples of appropriate controls for wet heating systems and their use in non-domestic buildings. An appropriate arrangement of hot water service system controls is one that is designed to the above guidance and also follows the advice in GPG 132.