Why MVHR is perfect for energy-efficient new build homes

We all want to ‘breathe easy’, to have good clean air in our homes. Increasing insulation and reduction of drafts contributes stuffy buildings and overheating.

Modern, energy-efficient homes are sound investments – good environmental credentials, quality build, utilisation of new technologies and lower energy costs – a win win situation for developers, landlords and tenants. When it comes to the indoor climate for a home of this type, there really is only one system that fits the bill. Michelle Sharp, Group Communications Manager at Zehnder Group UK, gives the lowdown on MVHR.

The greatest ongoing living costs for social housing occupants, after food, is for heating and electricity, therefore social housing providers should be investing in modern efficient systems such as Mechanical Ventilation with Heat Recovery that keeps the building well-maintained and keeps the money in the tenants’ back pocket – and in turn keeping houses rented for longer periods of time and reducing the risk of tenant complaint, issue and possible re-housing.

New homes are driven to be built to stringent energy-efficient standards and the choice of heating and ventilation system is crucial to achieve these standards and maintain a good, comfortable indoor environment. At the very top level is Passive House where MVHR systems are a prerequisite part of the build, and where amazing savings in energy bills can be achieved. We recently worked on a Passive House social housing development (Knight’s Place in Exeter – see case study below) that resulted in an annual energy bill of £18.00 per household! However, a home or a MVHR system does not have to be of Passive House standard to be beneficial for developers, landlords and tenants – it’s a perfecetly balanced solution for any modern, energy-efficient home.

So, what are these benefits, how are they realised and why should MVHR be the system of choice new build social housing?

It is the only Fit-for-Purpose Fabric First Approach

Build the structure well, with practically no air leakage and you will keep the heat in and the energy bills down. There is however the question of air – the air that the occupants will breathe, the quality of that air and how comfortable that air makes the home throughout the year. Going from a leaky house to a sealed house design will win the energy-efficiency agenda, but ventilation then becomes crucial to the home. An energy-efficient modern home needs a whole house ventilation system to contribute to the delivery of good indoor air quality.

  • Comfort: MVHR is a whole house ventilation system that provides continuous ventilation 24 hours a day, 365 days a year, working to maintain and deliver fresh air. It comprises a centrally-mounted unit which is located in a cupboard, loft or ceiling void, and which is connected to each room via a ducting network, with air supplied to or extracted from rooms via simple ceiling or wall grilles. Ventilation is balanced – extract and supply – so always a consistent level of fresh air! Air is extracted from wet rooms and supplied to habitable rooms.

    In winter, the heat exchanger in an MVHR system works to ensure that the fresh filtered air entering the building is tempered – making for a comfortable home and of course, energy efficiency savings. With frost protection in most units the unit is also protected from the extremeties of our winter weather! We talk about heat recovery, but an MVHR unit also plays its part in the summer - constantly monitoring the outdoor air temperature so that it can automatically make a decision to keep the indoor environment more comfortable. In summer, recovering heat isn’t necessary and will lead to discomfort and this is where the summer bypass is utilised to allow fresh air in, without tempering the air. The fresh air will give the perception of cooling to the home and tenant by circulating the air.

  • Energy Efficiency: MVHR helps reduce the heating demand of a property by recovering heat that would have otherwise have been lost through the traditional ventilation process. There are many different units with varying performances, but this can be up to an outstanding 95%!

    The nature of heat recovery also means that it contributes to reducing heating demands in the winter through the heat recovery process – this is a great contribution to the environment and the occupant who is living in the home!

  • Health: MVHR provides the continuous year-round ventilation which helps saves landlords from issues with mould or condensation. Mould and condensation are expensive issues for landlords and affect the well-being of tenants. There are over 5 million homes in the UK today suffering with these issues, most of which are a result of improved insulation levels and poor, not fit-for-purpose ventilation systems.

    MVHR provides fresh filtered air to dwellings – air is filtered through replaceable filters in the unit ranging from G3 to G7 depending on the unit, so that indoor air quality is consistently maintained. This is especially important with the increased density planning guidelines for homes and of course continued brownfield developments. Homes situated close to industrial estates, on flight paths and in and around busy roads may have poor external air quality levels which you don’t want to bring inside!

    According to research undertaken by Professor Hazim B. Awbi from the University of Reading on behalf of BEAMA, in order to avoid a serious and significant increase in asthma cases – which could be up to 80% and other health conditions related to poor indoor air quality and toxins in the air, homes must be adequately ventilated. He comments, “There needs to be increased awareness of effectively installed MVHR systems to prevent a rise in future health issues, particularly as UK homes become increasingly airtight and energy-efficient. I support the view that all new and refurbished homes should have effective and sustained mechanical ventilation installed as standard.”

Tips for specification

Heat Recovery Ventilation is detailed in Part F of the Building Regulations’ airflow rates, and helps efficiency via Part L, through SAP calculations. The decision isn’t a difficult one on the basis on energy performance, health and comfort. However it is more than an extractor fan and is the very heart of the home and therefore when looking at specifying MVHR you need to focus right from the design stage. Here are some top tips to guide you:

  • One essential requirement of MVHR is that the building is reasonably well sealed, with airtightness levels of 5 ach (air changes per hour) – there is no point putting sophisticated system in a leaky home.

  • The system should be designed from the outset as a complete package – the unit and the ducting - taking into account the performance of all components and materials to ensure they are compatible and meet the design requirements.

  • The choice of heat recovery unit must be based on a calculation of the floor area, the number of bedrooms, and occupancy levels – can the unit handle the pressure and deliver the airflow.

  • Look for systems that continue to filter the incoming air before it is supplied to the home when the bypass is open (especially important for allergy sufferers in the hay fever season).

  • Complaints about MVHR noise are almost always due to an under-sized system that has to work harder and more noisily than a larger system – don’t under spec to save space and money – it may be more costly in the end

  • When it’s time to install and commission the system, it’s essential to check that those doing the work are properly accredited and understand MVHR and its application. Installers of whole-house ventilation systems should currently have BPEC accreditation, though in the near future the requirement will be for installers to hold Certsure certification.

  • Handover and regular maintenance is essential for performance of the system in the home – look for a partner who will advise when filters need replacing and can offer training or support on when and how to complete the requirements

Get more advice

Manufacturers such as Zehnder provide an expert design service to ensure that the great results from MVHR are easily and reliably achievable. All social housing builders, architects, and building engineering services consultants are welcome to contact us for initial, exploratory advice. Whether your project is a new-build or an improvement programme for a modern building, there’s no point in throwing away energy, or making your building more vulnerable to condensation and mould problems when you don’t have to.  

Knight’s Place: Setting New Standards for Passive House within the Social Sector
Knights Place Housing is a sustainable social housing development of 18 one and two-bedroom apartments, designed by Gale & Snowden Architects for Exeter City Council. Built with meticulous attention to detail, the two blocks have been designed to strict Passive House standards, which deliver high comfort levels for residents via a mechanical ventilation and heat recovery system (MVHR). This produces consistent internal temperatures and excellent air quality whilst minimizing energy use for heating and cooling, resulting in lower energy bills. Knights Place is amongst the first multi-residential, certified passive houses in the UK.

Outstanding Energy Performance
Commenting on the specification of the products, Principal Mechanical and Renewable Energy Engineer at Gale & Snowden Jason Fitzsimmons explains: “Generally the key issue for passive houses is controlling heat loss through walls and windows. You can insulate but you still have fresh, cold air affecting the interior climate so the heat exchange efficiency rate of an MVHR system is very important.”
Knight’s Place apartments maintain a comfortable temperature of 21ºC year round for residents, with minimal heating required and low running costs. According to the SAP Energy Performance Certificate, dwellings at Knights Place can be heated for as little as £18 a year.

First published 26th April 2016.

image of Knights Place   image of a man blowing his nose   image of Michelle Sharp  
Knight’s Place, Exeter – an example of Passive House standard MVHR Installing a MVHR system will improve air quality and reduce the risk of health issues. Michelle Sharp, Group Communications Manager at Zehnder Group UK.