Comfortable Indoor Ventilation

MVHR Summer Bypass

A highly insulated and efficient home reaps reward form a MVHR system with the recovery of heat and tempering of supply air, but when it’s hot outside and inside, this isn’t needed.

A comfortable night’s sleep

The predictably unpredictable UK still brings spells of hot weather – a few days, a few weeks, or even months, - the rising temperatures create uncomfortable hot and bothered people in their homes, and especially during the night time.

The objective of the Summer Bypass is to not worsen the impact of hot weather – continue to ventilate and provide good levels of fresh air, without the heat recovery

It is crucial to understand how a summer bypass works on a unit.  They are all different, so it’s not just about ticking a box and saying the function exists. A summer bypass should help reduce the discomfort caused to occupants by hot weather, and the only way it can do this is by truly bypassing the heat exchanger and taking into consideration not only external conditions, but internal ones to.

What is a TRUE Summer Bypass?

The Summer Bypass must maintain ventilation performance to the home – not all units are capable or have been designed to do this.

A TRUE Summer Bypass is whereby intake air physically by-passes the heat exchanger.  The physical by-pass should be able to by-pass at least 90% of air volume flow.

Key Considerations

The Summer Bypass function is an important factor in helping deliver comfort, especially during the summer months, but remember, the MVHR system is still fundamental to well-being and good indoor air quality in an efficient and highly insulated home.

When looking at how a Summer Bypass works you should consider the following;

  • Does it maintain ventilation performance?
  • Does it filter supply air effectively?
  • Does it just activate and deactivate itself – if so, based on what?
  • Is it looking at external conditions only – what about inside the house?

Summer Bypass technology is not the same on every unit. Make sure you are choosing the most suitable for your application.

So, what happens when it gets hot?

The technology has evolved...

  • ‘It’s hot – slow it down’ – This approach is based on limiting airflow rather than stopping heat recovery
  • ‘It’s hot – send it away’  - This approach is based on physically by-passing the supply air and not recovering heat, automatically activating on an external temperature point
  • ‘It’s hot – but we knew that already’ – This approach is guided by a set comfort temperature which looks at temperature and humidity both internally and externally to maximise comfort
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