The importance of Post Occupancy Evaluation #POE #CaseStudy #Passivhaus

Posted onAuthorMark StephensLeave a comment

This post follows on from these:

The 1st County Mayo House added to Passive House Database

Why materials are important & embodied carbon calculations

Using DesignPH as part of the Passivhaus methodology

The reason that these posts (and this one) are that they all use the house we completed last year that was added into the Passive House database – you can read more about the project HERE and it was also featured on the Ecological Building Systems website HERE.

This post deals with ‘Post Occupancy Evaluation’ – ‘Post-Occupancy Evaluation (POE) is the process of obtaining feedback on a building’s performance in use’ BRE. You can read more about the importance of POE HERE.

As a founding signatory of Architects Declare Ireland, signatories are encourage to ‘seek to’:

Accelerate the shift to low embodied carbon materials in all our work – see the post above

Include life cycle costing, whole life carbon modelling and post occupancy evaluation as part of our basic scope of work, to reduce both embodied and operational resource use. – again see the posts above, and this one.

When the house was completed (October 2019) I placed a TinyTag data logger into a room of the building. This then measured temperature and humidity at intervals throughout the day and night. A year later (last week) I collected the logger and downloaded the data. At the same time I also gave the owners a questionnaire to complete asking about their perception of the house ‘in use’.

The blank ‘Room Comfort Questionnaire’ that we used can be downloaded HERE – a massive thanks to Sean Hogan at RKD with the help on this.

The graph below shows the raw data displayed in a graph of Temperature & Humidity & Dew point:

The second graph shows the interior temperature together with the exterior temperature (for the closest weather station):

The Passivhaus methodology includes three critical areas that relate to this blog post:

1. Temperature (Winter).

The interior design temperature used for planning & verification in winter (ie the heating period) should be on average 20C

2. Temperature (Summer)

For the summer (ie cooling period) a temperature of 25C is used. For Passive House verification, the maximum is 10% of the year that is > 25C

3. Humidity

The optimum humidity for thermal comfort lies within the inner circle of the graph below. The image below (credit at bottom of image) also shows the implications of too low or too high a humidity:

You can read more on humidity HERE

You’ll also see on the first graph the dewpoint temperature, the graph below (from Schoeck.co.uk) shows the relationship of dew point to temperature:

The Dew Point is critical in construction as it is: “The temperature below which water vapour in the air will start condensing to liquid. This is important in buildings, because anywhere there is a dew point, there is a risk of condensation and mold growth…” (Passive House + Magazine)

So. what do the results tell us:

1. The internal temperature does marginally drop below 20C in the winter period but on average for the year the temperature was 20.5C and you can see how the house coped with the fluctuations in external temperature in the graph above.

2. The percentage that the temperature was greater then 25C was 1.601% (Well within the threshold of 10% as a maximum for Passivhaus verification). Interestingly, the PHPP calculations had the % of overheating at 0.0% – I can only presume that this was caused by the significantly hotter summer and will be similar in years to come if we do not act on the climate emergency.

3. Humidity

The minimum humidity for the year was 28.25%
The maximum humidity for the year was 69.92%
The average humidity for the year was 47.40%

Most of the year is within ‘Comfortable’ and occasionally the humidity dips into the ‘less comfortable’ areas of the graph and all temperatures are well above the dew point temperature throughout the year.

On completion of the Thermal Comfort Survey, the perception of the temperature of the house in the summer was that it was overheating. The reality however was that it was only overheating for a much smaller percentage of the time.

There are some provisos I would like to give on this data which will give better results in the future for further projects:

  • The internal temperature was only taken in a single room. The room was chosen to receive a good amount of direct sunlight during the day and was next to the space used for a significant portion of the day. A detailed analysis would require data loggers in every room. There were restrictions on budget for this study. It may be that the over heating that was experienced occurred in other rooms. If the overheating does continue, possible remedies would be to provide external electrical blinds, brise soleil or additional planting.
  • The external temperature was extracted from the closest weather station (Belmullet), similar data was also taken from the weather station at Claremorris. The principle difference is that the minimum temperature at Belmullet did not drop below 0C due to its coastal location (which Claremorris did). A more accurate analysis would require an external data logger – there would be one for the heat pump but I did not have access to this data.

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