Commercial MVHR

Good indoor air quality and climate in schools has a positive influence on the learning and teaching environment, whereas a poor indoor climate leads to reduced performance and in extreme cases can even cause illness. Especially in winter, schools with conventional window ventilation experience high heating costs, if they want to offer pleasant room temperatures and good air quality. The immediate effects of poor indoor air quality can be headaches, drowsiness and a lack of concentration. A 2008 study of the University of Reading revealed that lowering CO2 levels to 1000ppm in class rooms improved the student’s performance by up to 15%. The long-term effects are more severe, especially as they affect children’s lung development.

In the crowded classroom situation, the air quality is primarily influenced by the fresh air requirement of the pupils.
Comparing CO₂ levels and temperatures in classrooms with windows closed and windows opened at a certain time, following graphs of CO₂ levels show that the air quality is sub-standard. the graphs relate to a school built in 1985 (BG Dornbirn) with a class room volume of 225 m³ and an average natural infiltration rate of 0.14/h.

Even with occasional window ventilation in the classrooms – in the breaks, ventilation approx. 20 to 25 minutes after the beginning of teaching – compliance with the limits of 1000 to 1500 ppm CO₂ in the classes was barely possible, with CO₂ concentrations increasing to 2500 ppm. Long-term measurements in schools often show values ​​of around 3,000 to 4,000 ppm CO₂ in the classrooms and “peak values” of up to about 5,000 in conventional ventilation behavior up to 6000 ppm.

The IAQ in classrooms affects the cognitive function of the students and pupils, reflected in their test results.

• Children perform schoolwork 12% faster and 2% more accurately when the outdoor air supply rate is such that the resulting CO₂ concentration in a typical classroom is 900 ppm instead of 2,100 ppm (Wargocki et al., 2020).
• School test and examination results are 5% better when the outdoor air supply rate is such that the resulting CO₂ concentration in a typical classroom is 900 ppm instead of 2,400 ppm (Haverinnen-Shaughnessy et al., 2011; Wargocki et al., 2020).
• National test results are 5% better with a 7.5 L/s/p than with a 2 L/s/p outdoor air supply rate in classrooms (Haverinnen-Shaughnessy et al., 2011, Mendell et al., 2016; Wargocki et al., 2020).

Schools and nurseries need a good indoor climate with adequate ventilation to maximize the well-being and avoid related drops in concentration levels or sickness.

Correctly designed and installed MVHR systems provide these healthy environments in an un-intrusive way and reduce the heating costs at the same time. A mixed ventilation strategy of MVHR and natural ventilation can be incorporated in order to reduce capital costs.

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Heat recovery systems are an ideal solution for offices. The necessary ventilation requirements can be fulfilled with great savings in heating costs. For airtight buildings about 30% on heating can be saved.

Adequate ventilation is an important factor to avoid drowsiness and lack of concentration. On the other hand should cold drafts be avoided, which can cause sickness.

In comparison with air conditioning for offices, HRV systems use only little energy and don’t re-cycle any air, which can have health implications, if the air conditioning system is not serviced regularly. HRV systems often provide no active cooling, as AC systems do. This again lowers the energy demand, but makes it necessary that the architectural design shields the building from excessive solar gains, e.g. by natural summer shading. Paul HRV systems come with an automated summer bypass, that brings in un-pre-heated air from the outside when the internal temperatures exceed a certain threshold. The system goes back in heat recovery mode when the temperatures drop below the threshold.

Several Passive House offices have been built in the UK in recent years, some of them with Paul Maxi HRV systems. The feedback shows that the temperatures remain comfortable in summer, if the ventilation is high enough.

The ventilation requirement is mostly depending on the number of people the office is designed for. A guideline value for the fresh air supply is 30-36 m3/h per person.

Heat Recovery Ventilation is an excellent solution for care homes and retirement homes, especially in conjunction with Passive design.

Occupants and staff benefit from continuous comfort ventilation with HRV:
– No cold drafts
– Continuously fresh air supply
– Warm environment
– No build up of smells and other pollutants

Several Passive House care homes have been built across Europe with HRV systems. Besides tremendous savings on heating energy, occupants and staff alike felt the completely different indoor climate, compared to conventional care home buildings.