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Mechanical Ventilation and Heat Recovery (MVHR)

MVHR – Mechanical Ventilation with Heat Recovery is exactly that! It provides a balanced ventilation system and clean air, whilst retrieving most of the heat from the stale air which is pumped out of the building.

Environmental considerations are driving building standards and practices towards better insulated and more airtight properties with little natural ventilation. However this does provide a challenge, as damp stale air can lead to mould formation and condensation problems, and a generally unhealthy indoor air quality.

MVHR is not only an elegant solution to this predicament, but within the framework of government commitments to reducing carbon emissions and improving the energy efficiency of buildings generally, it also ticks all of the right boxes!
Whilst this will gain the relevant SAP points to comply with parts L and F of building regulations for those who are embarking on new build or major renovation projects, the real benefits will be more tangible in the ‘fresh air’ environment within the building. Any potential moisture or odour issues are alleviated without losing the heat from a building. Compared with the traditional approach of opening a window, (or more latterly the mandatory use of unsightly trickle vents in windows) this maintains airtightness and retains the heat.

Mechanical ventilation and heat recovery

The MVHR system essentially consists of a central ventilation unit and heat exchanger with ducting taking the stale warm extracted air from the kitchen, utility and bathrooms to outside. The heat is transferred to fresh air from the outside and sent back down into bedrooms and living rooms. As much as 90% of the heat that would typically be lost in traditional ventilation, can be recovered in this way and recycled. At the same time, fresh air is continuously brought in from outside and filtered to remove particles such as pollen, particulates and insects etc, before it passes over the heat exchanger and is distributed through to the rest of the house.

MVHR schematic

A ventilation system can be for the whole house, or strategically targeted at rooms such as bathrooms, kitchens and utility rooms which are more likely to have problems with moisture and odours. In this way it is a much more efficient and quieter successor to the standard bathroom extractor fan. It also helps to protect the fabric of the building. In the summer, the heat exchanging element can be bypassed for air cooling and can reduce indoor temperatures in the same unobtrusive way.

Orangehouse have installed ventilation systems in a range of house types including an eco-house with a Rehau buried earth duct air supply!

However, as with any heating/cooling system, there is a range of products and system designs, both in terms of quality and price. Here at Orangehouse we mostly use the Systemair range of products. We work closely with Systemair from the earliest design and quotation stage to produce a bespoke system, which optimises efficiency whilst keeping noise to a minimum. The main units can be sited in a range of locations such as lofts or utility rooms while the integrated controls allow for flexibility of use, including a summer bypass.

As MVHR is a relatively new technology in the UK, there can be a wide range in terms of the quality of the installations, leading to issues over leaking condensation, poor air circulation, noise and excessive use of electricity. It is important to determine that the installers are competent, right from the beginning of any project.

MVHR orangehouse installtion

In principle, good MVHR design should encompass the following framework

  • Optimise the efficiency of the heat recovery.

  • Minimise electricity used by reducing pressure losses within the system.

  • Minimise noise emissions from the air handling unit and “interference” from other rooms, and mitigate mechanical vibration and air turbulence within the system.

  • Use best practice installation methods and airtight products, to ensure that the air is delivered where required and hence avoid problems with noise and condensation.

  • Use durable products and fixings to ensure the ducting will last the lifetime of the building.

  • Deliver good quantities of air to each room to ensure healthy humidity, oxygen and carbon dioxide (CO2) concentrations and low pollutant levels.

  • Ensure that condensation both inside and outside the ductwork is dealt with properly.

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