Heat Recovery Ventilation Explained - Design Principles

Mechanical Ventilation systems with Heat Recovery are becoming more popular nowadays. But what exactly is heat recovery ventilation (HRV), what's the difference from energy recovery ventilation (ERV) and how should this system be designed to function properly and avoid too high investment costs?
✅ Are you an architect, engineer, or builder who wants to learn to design and build energy-efficient, healthy and affordable Passive House buildings?
👉 Click here to read more and become a Certified Passive House Designer/Consultant: passivehouseschool.com/course...
📞 Want to learn how you can start designing Passive House projects and become a worldwide accredited professional? Book a FREE discovery call with me - passivehouseschool.com/call/?...
----
My name is Anton Dobrevski and I'm an architect and accredited Passive House Trainer who is passionate about designing High-Performance and Healthy buildings. On this channel, I'll be talking about Building Science and the Passive House Standard, more specifically about Insulation, Airtightness, Vapour Control, Heat recovery ventilation systems, Thermal bridge-free designs, Fresh Air, Healthy Buildings, Comfort, Innovative Building Products, and I will show you around some of the projects I am working on. You'll also find videos revealing the thinking, the process, and the ideas behind the making of Passive House buildings. If you are an Architect, Engineer or Builder hit that subscribe button!

[@vincentshapland7250]

Great video. HRV with summer bypass is also essential to prevent overheating within ground floor bedrooms during the night, as windows can't be opened for security reasons, as stipulated within Approved Document O.

[@AntonDobrevski]

Thanks, Vincent! A summer bypass is indeed very important as well. Most of the high quality units have a summer bypass.

[@vitoshabg]

Very interesting video! Can you recommend a counterflow HE? The majority seem to be crossflow. What about ERV, is there any model/series you can recommend which is available in Bulgaria?

[@AntonDobrevski]

Thank you! You should check out Zehnder. They are one of the best performing units on the market, all their units are PHI certified (i.e. have guaranteed efficiency within a working range) and that's why we use them for all our projects. Furthermore, they have ERV versions and are available in Bulgaria.

[@philipp.]

Excellent content! About supply and extract zones on different slides of house. Is it necessary to have vents on doors?

[@AntonDobrevski]

Thank you, Philip! When using the cross ventilation principle you will either need door vents, gaps under the door or dedicated transfer air grilles in the walls.

[@vitoshabg]

How do you calculate what the gaps under the doors should be?@@AntonDobrevski

[@AntonDobrevski]

@@vitoshabg To achieve air speeds below 1 m/s, we multiply the volume that has to pass through the door by 2.78 and this gives the area of the gap under the door in square centimeters

[@tealkerberus748]

Speaking from personal experience, the supply and exhaust need to be balanced for every room. Otherwise as soon as someone closes the door/s to that room, the air movement is going to slow or stop, because the only way for air to get from one room to the next is under the door. If there's a draught under the door, you'll get that much air movement, and if the door is fitted not to have a draught, you'll get no air movement at all. Closing the bathroom door while we're using the shower or toilet, or closing the bedroom door at night, is normal human behaviour. Humans like privacy in these spaces, and the closed bedroom door is a "do not disturb" sign that even cats have to respect. The ventilation needs to be built on the assumption that when ventilation is most needed, the door will be shut.

[@AntonDobrevski]

To avoid oversizing the system, paying too much for ducts and drying out the air inside, supply and extract should be separated in two different zones according to the cross ventilation principle. To allow the air to move freely even at closed doors, are provided transfer openings either at the doors or in the walls. These openings can be designed to avoid the transfer of noise/light. The air volumes are quite low and don't cause any drafts (with the right seizing of the openings).