Is MVHR Truly A Low Energy, Low Cost, Sustainable Ventilation Strategy?

03 Jun 2021

MVHR or Mechanical Ventilation & Heat Recovery works on the principle of extracting and re-using waste heat to pre-warm and filter fresh air around the property. More than 95% of the waste heat can be recovered in this way… But are we focusing too much on the benefits of heat loss recovery and missing the significant drawbacks to long term sustainability.

The upfront costs are high, to ensure you are achieving low energy MVHR solutions, the best models are required. This involves significant equipment, including sensitive sensors and digital controls. Then there is the ducting, which should be insulated and achieve exacting tolerances to ensure performance. Bad installations, low grade ducting will negate the benefits you believe to be gaining.

  • Do we really know what equipment is being put inside the walls and soffits of our buildings?

  • Do we really consider the ongoing costs of running and repairing these large installations of inaccessible parts?

Natural ventilation (such as window vents) however continues to be a low cost, low energy and sustainable strategy for our buildings. With new product advancements, we have more and more options and reasons to use this strategy… So why aren’t we, perhaps that is a question we should be asking ourselves?

The Importance of Ventilation in Schools

Poor indoor air quality in schools; every time we breathe in polluted air, our lungs take in microscopic particles and pass them through the bloodstream. This can lead to a variety of health problems;

  • Asthma and allergies

  • Irritation of the eyes, nose, and throat

  • Headaches, dizziness, and fatigue

The UK has one of the highest prevalence rates of childhood asthma among European countries, with almost 10% suffering from asthmatic symptoms.

Ventilation in schools in the UK

Research shows that returning to school in September triggers of asthmatic symptoms for children.
We know that school performance drops drastically at high temperatures with dirty air that is not ventilated, having a major effect on concentration levels.

Building Bulletin 101 Ventilation of School Building - Average fresh air rate within your school should be at least 5 litres per second per person. The purge rate fresh air rate needs to be 8 litres per second per person for all new building spaces. CO2 levels should average below 1,500 parts per million and for mechanical CO2 levels should average 100ppm.

  • All occupied areas in school buildings shall have controllable ventilation at a minimum rate of 3 litres of fresh air per second for each of the maximum number of persons the area will accommodate.

  • All teaching accommodation shall also be capable of being ventilated at a minimum rate of 8 litres of fresh air per second for each of the usual number of people in those areas when such areas are occupied.

  • All washrooms shall be capable of being ventilated at a rate of at least six air changes in an hour.

  • Adequate measures shall be taken to prevent condensation and remove noxious fumes from every kitchen and other rooms in which there maybe steam or fumes.