Thursday, 29 November 2012

Evolving an NZ home into a European one

I've been meaning to share this for ages. 

I recently bought a house in New Zealand after living in Europe for nearly a decade. This caused a slight shock to my system. European homes are warm, New Zealand homes are not. My house is a fairly typical 1950s bungalow, it had no insulation in the ceiling, walls or underfloor, no double glazing and no central heating. There is a heatpump attached to the wall but without insulation one is trying to warm the environment as well as ones house when it is on. Since I'm a miser, this makes me mad. So I've tried to do something about this. 

Consequently, we added insulation to the ceiling (Terra Lana), underfloor (Autex) and a moisture vapour barrier was laid on the ground under the house. A week later the single-glazed windows in the house were removed and replaced with double-glazed windows by Thermoglaz. Their method allowed us to retain the character of the original wooden frames. The timing also allowed me to collect temperature recordings in our house as uninsulated, insulated and insulated+double-glazing. We also changed the way we used the heat-pump this last winter (2012). We now leave the door open from the living room and the heatpump on low over night. So, I included some of this data too. 

The data plotted here was collected in my bedroom using a "weather forecast multi-channel in-out thermometer with cable free sensor and radio controlled clock" (model TTN302). The data was chiefly gathered over the winter of 2011 in Christchurch, NZ. 

As you can see, insulating the house made a significant improvement to the internal room temperatures. Prior to adding insulation I had been putting my children to bed in a room that was 5°C or less. Roughly the same temperature as your refrigerator! No wonder illnesses are so prevalent in NZ. The insulated house temperature improved markedly, but still only by +3°C or so.

Flushed with this success we hoped that double-glazing all of our windows would make a similar improvement. Unfortunately, double-glazing our house made no apparent difference. Since the cost of double-glazing is more than twice as much as insulation, this was a bit irritating (says the miser in me). Double-glazing did appear to reduce the amount of condensation inside -- but I haven't been measuring that -- also, I've been running a dehumidifier which has probably helped too. Next time I think we'll just buy some very good drapes and a dehumidifier instead of double-glazing, saving a huge amount of money.

Finally, changing our heatpump behaviour made a major improvement too. While our bedrooms were rarely at an ideal room-temperature of 20°C they were vastly more comfortable than when we first took over the property. 

I hope these notes will help inform other home improvers, saving a lot of money and increasing the health of NZ families. 


  1. What are the dotted lines showing?

  2. Insanity?
    I forgot to mention, the data and code is available here:

    Pamela Williams requested functions fitted to the data. I went with a non-linear model y= A/(1+exp(C*x)). I don't recall the logic behind why I used this function.

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