Principles for reducing building energy demand and emissions

and emissions from buildings over their lifetime, this study has considered only the energy and emissions during the operational phase of the building. It has addressed all thermal energy sources, sinks and heat transfer within the building (including heating and cooling, ventilation and air conditioning, lighting and electrical power etc.). Cooling demand cannot usefully be considered in isolation and can only be accurately assessed by taking into account all sources of heat generation and removal, both within the building and between the building and its external environment.

Cooling and heating energy demand are generally not independent of each other, since a change that reduces the heating load (for example increasing the insulation in a building in order to reduce heat losses) could increase the cooling load in the summer due to an increased risk of overheating. Conversely, reducing internal heat gains in a building (for example, by moving to more efficient lighting and IT equipment) will reduce the cooling load in summer but increase the heating load in winter. If the key objective is to reduce the total emissions from a building, it is necessary to assess both the cooling and heating energy demands and to sum the emissions associated with both, to determine whether a planned change will actually reduce the total emissions. All of the internal heat gains associated with human occupancy, lighting, ICT and other power loads must also be included in the calculation, since they can all impact the net heating and cooling loads.

In any cooling or heating application, the primary energy input and associated emissions might be reduced by:

1. Increasing the efficiency (or COP) of the cooling or heating system

2. Reducing the thermal load through other improvements (such as changes to a building’s design features or operating parameters)

3. A combination of both of these measures

The indirect emissions could also be reduced through the use of greener (lower carbon) energy sources, which could be cleaner fossil fuels or electricity from renewable sources. There may also be scope to lower the direct emissions by reducing the refrigerant leakage in RACHP systems and by using lower GWP refrigerants, as discussed in Chapter 4.

Opportunities to reduce the thermal loads for RACHP systems depend on the application, the system installation and the operating environment. In recent years significant efforts have been made in supermarkets to reduce their energy use through measures that include adding doors and lids to freezer and refrigeration cabinets, replacing filament lamps with low energy LEDs, improving the insulation and efficiency of equipments and better temperature control (which may permit higher storage temperatures for some products). At the same time, improvements in compressor design, alternative refrigerants and optimisation of setup parameters have helped to increase the COP of these systems.

Measures to reduce the carbon emissions associated with the cooling and heating of buildings (whether using RACHP or other technology) might include:

 Reducing the thermal loads associated with the building fabric, through more efficient building design. Modern Building Regulations play a key role here, although they have until recently tended to focus more on heating energy than cooling.

 Modifying the thermal mass of a building, either by increasing it to reduce the sensitivity of the internal environment to a rapidly changing external environment, or alternatively by reducing it to achieve a faster thermal response, for more precise control of the internal environment.

 Storing thermal energy (within the building or a separate store) for later release.

 Reducing the internal heat gains (and losses) associated with the heating, cooling and ventilation systems, occupancy levels, lighting, ICT equipment, and other power loads such as lifts, hot water, refrigeration and cooking.

 Changes to the building management system (BMS) and operational parameters (e.g. the use of pre-heating and cooling, temperature set points etc.).

 Recovering and re-using energy that might otherwise be discarded from the heating and cooling systems and exhausted into the external environment.

 Making use of ‘free’ cooling, night time cooling and natural energy sources and heatsinks (e.g. ground, rivers and acquifers).

 The adoption of modern low carbon cooling technologies (e.g. low GWP refrigerants and high efficiency compressors).

 The use of low carbon electricity (from the national grid or decentralized local power generation) and renewable energy generated onsite.

 In cities, reducing the impact of the heat island effect through measures such as increasing vegetation and evaporative cooling, as well as by increasing the albedo (solar reflectivity) of the urban environment to reduce the absorption of solar energy

5.1.1 Building design and comfort levels

Factors that influence the heating and cooling energy demand and emissions from buildings include:

 The building design, orientation and construction materials

 Glazing, solar gains and shading

 Density of occupation and occupancy profile

 Ventilation, heating, cooling and hot water systems and controls

 Internal heat gains (people, lighting, IT, small power, catering, machinery etc.)

 External environment (daily and seasonal weather), comfort levels and set points

There may be further opportunities to reduce carbon emissions through passive cooling methods and the inclusion of renewable energy technologies, also to make improvements over the life of the building, particularly during renovation or refurbishment.

Opportunities may also exist to reduce heating and cooling energy demand and emissions through adaptive control of temperature set points (adjusting the set points according to the external environment). Figure 5-1 indicates that for any given outdoor air temperature there is a wide range of indoor temperatures that are considered acceptable by the majority of building users, the 90% acceptability window being more than 5°C wide. Set points could therefore be adaptively moved towards these limits as the external environment changes.

Figure 5-1. Acceptable operative temperature ranges for naturally conditioned spaces [Source: CIBSE (2013)]

Whilst the principles behind reducing energy demand and emissions are straightforward, the relative merits of alternative design approaches and other measures can only be assessed accurately through the use of building simulation and energy analysis software tools.

5.2 Energy modelling methods and software tools