Designing for Summer Comfort

A misconception has grown recently that low energy houses are somehow more prone to overheating than ‘traditional’ houses. There have been a number of newspapers quick to publish lethal eco home overheating headlines.

This masterclass examined how to design for summer comfort, an issue that is not just specific to Passivhaus projects, but one that should be applied to all designs.

Topics covered during the event

• Summer comfort and the PHPP overheating criteria

• PHPP v dynamic models

• Overheating energy balance – gains and ventilation

• Summer internal heat gains (IHG) in PHPP

• Summer ventilation in PHPP

• IHGs – impact and examples

• Thermal mass and dense insulation

• Glazing; shading, orientation

• Fixed shading – effective solution with caveats

• g-value – summer winter payoff?

• Design approach & responsibilities

• Active cooling in the UK?

Comfort assumptions, benchmarks & criteria

Delivered by Nick Grant & Mark Siddall, the Masterclass began by breaking down what is optimal thermal comfort and questioning how hot is too hot?

Overheating is not solely reliant on temperatures, relative humidity and ventilation are also involved. Designers must be conscious of theory and reality in regards to adaptive comfort. There is a temperature range that is acceptable for human comfort, but age, health and fitness all play a part in what we perceive as optimal adaptive thermal comfort. Psychological attitudes can lead to a 'Goldilocks syndrome... my house is too hot, my house is too cold.'

PHPP overheating criteria

Passivhaus designs to a simple standard benchmark rather than dynamic climatic models that predict future scenarios. The recommended tolerance for temperatures to be over 25C should be less than 10% of the year, as set out by the Passivhaus Institue.

Design for Delight

The speakers stress it should be about building buildings that work, not scraping by with minimal building regulations. PHPP allows designers to stress test ‘what if’ scenarios, that can flag up potential risks and check the robustness of their designs. This allows analysis of extremes and all the variables in between.

Some buildings will require, or even be reliant on lots of ventilation/cooling, and that is ok, as long as these issues are explained clearly to clients/occupants. Night ventilation can solve many issues but is not always appropriate due to noise, pollution or security issues which can lead to insurance problems. Context is highly important and must be taken into consideration. Multi-occupant dwellings can cause much more concern than an individual house.

You can do things well, cheaply, or quickly, but its hard to acheive all of them simultanously. Be transparent about design assumptions relating to comfort expectations and any limits or requirements on the building occupant’s behaviour.

summer comfort masterclass: Design Choices


Enthusiast Occupant	High cost, low input	Embrace design constriants	Failure

User behaviour

3 case studies with post-occupancy monitoring data were examined for overheating issues, potential causes and recommended solutions. They highlight the impact of occupant behaviour, and that there will be scenarios that you have not thought of.

Overheating can occur in winter due to over compensation during the heating season!
Blinds and shutters in the UK are used for privacy rather than for shading. Changing habits and culture is difficult to do.
The perception of control and its effect on occupant comfort can be significant as mentioned above.
Try to design buildings that work simply rather than rely on fancy equipment.

Passivhaus Masterclass: Summer comfort

Key Considerations

•Glaze for daylight and views not solar heating.

•Target window area about 20% of TFA – Rules of thumb.

•Glass below 800mm has no daylight benefit.

•Do the numbers, your intuition will probably be wrong!

•Design for summer delight not minimum targets.

•PHPP is to help you design not a test to scrape through.

•Stress test your design and be clear about assumptions.

•Prioritise unwanted gains reduction.

•Ventilation is good but you can’t always rely on it.

•As ever, KISS (Keep It Simple Stupid).

Check out our guide How to build a Passivhaus: Rules of thumb, for some pointers on overheating. Be sure to keep an eye out on our website for upcoming Masterclass events and join up to our newsletter to keep abreast of the latest UK Passivhaus developments.

24th February 2016

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