Building Services Design Considerations
The residential sector continues to become ever more onerous with a focus on energy efficiency and reducing emissions. This is demonstrated in the level of information expected in ‘Energy Statements’ that we prepare for planning submissions.
To provide some insight in to how this sector is developing, with regard to environmental design and building services, we review below some of the topics that are commonly discussed on projects.
Setting out to provide a building fabric that complies with the thermal requirements of the Building Regulations is; I am afraid, not good enough to achieve compliance. The ‘U’ values for the building fabric generally need to significantly lower than the minimum standards specified; especially with Local Authorities beginning to stipulate that building emissions need to be 40% lower than Building Regulations targets.
SAP calculations, used to calculate the energy efficiency of dwellings, take into account the heat loss through thermal bridges, where there is unwanted heat transfer through joints in the structure or a building element. We recommend that buildings are constructed to ‘accredited construction details’ to limit thermal bridging but to take full advantage additional calculations need to be made in the SAP calculation process. An improvement of around 3% can be achieved where calculated values are used in lieu of default values.
Air Tightness & Ventilation
Limiting building infiltration and providing controlled mechanical ventilation has already made a big impact on occupant comfort, reducing energy consumption and preventing condensation. Whilst the standard required is 10m3/s/m2 at 50Pa the minimum recommended is half of this value with mechanical extract only systems. If the air tightness is reduced further mechanical supply and extract ventilation systems should be considered.
Centralised ventilation systems have the significant benefit of reducing the number of façade penetrations whilst maintaining a continuous low level ventilation rate, these systems can automatically respond to an increase in humidity when an occupant uses as shower for example.
Centralised supply and extract ventilation systems now have much improved heat recovery capabilities with up to 90% of the waste heat being recovered. These systems have the added benefit or removing the need for trickle ventilators in windows or wall vents from being required.
Low energy lighting (e.g. compact fluorescent) is now standard in new homes and LED lighting has bridged the gap that low voltage lighting used to fill where feature lighting is required. To meet aesthetic and user needs consideration must be given to where dimming is required, for example in living rooms and bedrooms, where a mix of these light sources is required. Light switches have advanced such that dimming, scene setting and remote operation can now be achieved at a low cost.
Heating is where the biggest changes are taking place. The move away from local boilers within apartments continues with communal systems becoming more common place and providing many benefits, including Low Carbon energy production via integrated CHP.
In apartment blocks this has helped improve buildings by removing noise from boilers in kitchen/living room areas, avoiding access panels in ceilings for flue inspections, removing the requirement for flue penetrations in walls and unsightly flue discharges.
Electric heat pumps have become more popular with both local and centralised systems on the market. Exhaust air source heat pumps in apartments are being installed but are best suited to smaller and highly insulated apartments with under floor heating. Communal heat pumps systems may have refrigerant pipework routed through the building serving interface units in apartments which provide conventional heating and hot water. The issue with communal heat pumps is often the space required for external plant and dealing with any noise issues.
Communal gas heating systems should consist of a mix of condensing boilers and a combined heat and power (CHP) unit. The CHP would meet around 50% of the buildings annual heat demand. CHP manufacturers have responded to the market with smaller, modular, units becoming available. The requirement for thermal storage needs to be considered to even out hot water load profiles when optimising CHP usage.
Within apartments served from communal heating systems it is now normal for a heat interface unit (HIU) to be provided which would accommodate heat exchangers, pumps and meters for energy billing. From these units a conventional radiator or underfloor heating system would be installed.
Much debate has taken place with regard to domestic hot water from communal systems. Hot water can be generated at the HIU, much like a combi-boiler, or a small hot water cylinder with fast recovery can be provided increasing the quality of the system, providing resilience and thermal storage to allow CHP plant to run for longer.
Use of PV (Photovoltaic cells) has become increasingly popular as the preferred default when using CHP due to ease of installation and integration into the building’s services systems.
What Flatt Consulting can do for you….
We design central energy networks for multi-apartment residential developments and commercial developments – including all associated energy reports and building services design.