In Depth

Benefits of MVHR

MVHR is becoming increasingly common due to the demand for more energy efficient properties.  With correct installation and minimal understanding by the eventually occupier any property with an MVHR running with have a range of benefits - impossible with any other ventilation system or technology. 

Feel the difference in a more comfortable, peaceful environment and then see the difference in your energy costs.  The main benefits of MVHR are:

• Allergies – all internal air is filtered.  Because of the high specification of the filters many airborne pollen or allergens are kept away from internal living areas. Asthma, hay fever and many serious allergies are often worse at home.   Anyone suffering from any allergy would feel far better in a controlled air environment.
• Moisture and humidity – The “wet” rooms are the rooms MVHR are continually extracting from.  Many properties have moisture issues in some form.  Condensation, mould or damp are the unwelcome results.  Even when there are no visible signs, the moisture content of the air can have an effect on the property and the occupiers. As an example dust mites prefer humidity. 
• Smells – A smell after cooking, cleaning or smoking will linger if the air in a property is not constantly replaced.  With no need to open windows, even for the “fresh air feeling”.
• Fresh Air & Peace and Quiet – as well as being healthier, less smells and better humidity the moment the system is turned on you will feel the difference.  After a short time the air temperatures will stabilise and it will feel more comfortable.  As the property will be well insulated and sealed, no external noises can be heard.  Easy to understand how this has such a positive effect on a property and the people within it.
• Heating costs and sustainability – when the heat is kept within a property and recycled there is a noticeably difference in heating requirement.  This is a key advantage for anyone looking to improve the efficiency of their home of working environment.  For the same reason you can be assured you are doing your bit for the environment and CO2 footprint.

Detailed understanding of MVHR

Mechanical ventilation and heat recovery is the optimum ventilation system solution for energy saving properties. Many installations often surpass building regulation requirements. There are a number of other benefits from MVHR through the automatic control options, again set at commissioning.  Understanding these can add to the advantages of the system for all times of the year and occasions.

Control aspects

Summer bypass – Heat recovery is not always an advantage.  During summer months the air is bypassed from the heat exchanger with temperature control settings.

Humidistat – often we install a humidistat within the extraction system so the unit will boost air movement when the humidity levels rise.  The number of hourly air changes within the property increases and ensures the property is quickly back to the correct humidity levels.

Localised boost switches – the MVHR system should have a function to be boosted when required locally to “wet” rooms. One option for achieving this is installing boost switches immediately outside bathrooms to boost the unit.  This is a timed feature, set on commissioning. Once activated the unit boosts for a period of time and automatically switches off.

CO2 sensors – although less common, a CO2 sensor within a system will control the speed of the fans from the CO2 levels within a property.  Useful if the number of people within the property is often changing (e.g. Hotels).

System Balancing

Properly balancing the system once installed ensures the correct volume of air is drawn out of kitchens and bathrooms within the guidance of building regulations. Fresh supply air is blown into living rooms and bedrooms for maximum comfort. 

Correct balancing will ensure well used or larger areas do not suffer with less air changes and lesser used rooms such as spare bedrooms are not wasting energy in higher than needed ventilation rates.

Insulation and airtightness requirement

MVHR systems, particularly whole house, require higher insulation and airtightness levels than a standard property.  What this means in reality is, if you fitted an MVHR within a property that did not have the correct levels, the benefits would be lost in the fabric of the building.  For this reason MVHR must be properly considered and understood before installation.  That said, almost all new homes now would see the benefits of an MVHR and many have then installed as standard.  For one off projects and renovations the MVHR often comes as a result of the insulation and airtightness levels rather than the other way around.

In reality, this is often done at design stage and fits within the SAP calculation for the property.  An energy consultant is required for this but the benefits of including an energy consultant in the early stages should pay off in the long run.

As a rule of thumb an MVHR will be effective at an airtightness level lower than 5m3(h/m2) at 50Pa.