Tom King, a trainee sustainability consultant at GreenBuild Consult, explains how Waste Water Heat Recovery Systems (WWHRS) can help with Part L Compliance.

Waste Water Heat Recovery Systems (WWHRS) are simple, energy efficient devices that can be fitted onto showers and baths to heat incoming mains water, which reduces the demand on other water heating systems.

As the adjacent graphic demonstrates, warm waste water from a shower or bath enters a heat exchanging copper pipe that runs alongside and preheats the incoming cold mains water.

Installing a WWHRS can be an effective method of achieving compliance with UK Building Regulations Part L for new build residential developments and can also help to reduce energy costs.

In order to achieve building regulations compliance, the calculated dwelling emission rate (DER) must be less than the target emission rate (TER). If dwellings are not achieving their target score they would benefit from incorporating WWHRS into the design stage specification to improve performance in SAP calculations – since they reduce the DER.

Such systems could also reduce or potentially eliminate further requirements to improve the building fabric or other system efficiencies.

Notional calculations were carried out to demonstrate the impact of WWHRS on SAP results. Following the installation of a mid-range WWHRS (operating efficiency of 60%), a 100sq m two-storey detached house achieved an improvement over Building Regulations requirements from 0.1% to a 4.6%.

The overall percentage improvement depends on several other factors. The primary influence is the hot water demand of the dwelling, which is determined by floor area, heating systems and building fabric efficiency.

A large dwelling, for example, will have increased demands on hot water, which will require more showers and baths to have WWHRS installed to achieve the same percentage reduction as a smaller property with just one shower.

Installing WWHRS can be beneficial in new build properties when it comes to selling or letting the property. By improving energy efficiency, running costs will be reduced, which would also make those properties more attractive for potential buyers or tenants.

WWHRS can also help to achieve Part L compliance since they reduce the DER of dwellings and could be a more cost effective or practical solution than other options, such as increased insulation, improved heating systems or installing renewable energy technologies.

GreenBuild Consult’s experienced sustainability consultants can advise on the impact of WWHRS in SAP calculations, as well as providing a range of compliance options for the design stage or at the as-built stage of projects.

GreenBuild Consult offers full Part L compliance and EPC services for domestic and commercial properties; the company can advise how best to meet regulations and improve energy performance.

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For all enquiries, send an email to Lisa Williams or call: 0333 355 3610.