Monday, July 16, 2012

Low Carbon House Renovation

Given my energy background, it was natural that I would set about improving the energy performance of my house when I moved in over 18 years ago. It is a detached bungalow built just before the first  the reductions in energy use I have achieved (about 75% in the last 14 years) have come in several phases.

Following the large reduction in gas usage in 2007, and the subsequent installation of solar systems in 2008 and 2011, I have begun to focus more on my carbon footprint rather than just energy reduction. Now that my carbon emissions are barely 300 kg/year (most houses are measured in tonnes), I think it is reasonable to refer to my low carbon house and since I've passed the 90% renewables contribution landmark I've even allowed myself to start thinking of the Holy Grail of Zero Carbon! The graph below shows the contribution of the different renewables over the past 12 years.

Prior to 2009 I had reduced the heat losses through roof, walls, doors and windows substantially over a period of years. The large reduction in gas usage in 2007 came from a combination of disconnecting the underfloor heating in my conservatory (and sacrificing some tender plants) and pumping foam insulation into the 9" hollow block walls. The reduction in gas usage in recent years is due to the fact that I have been decommissioning my central heating system room by room as I have worked my way through the house putting in underfloor insulation and sealing off each floor with Intello airtight membrane (  Only the sitting room now remains for this treatment in 2013.  Each of these rooms now has a Süka wall-mounted electric heater which is thermostatically controlled and I have each one on a timer suited to the usage pattern for that room. 

Installation of underfloor cellulose insulation and Intello membrane

In March 2011, I had an air tightness test conducted by Christ Spoorenberg of EcoScan. The results were a slightly disappointing 7.68 Air Changes/Hour @ 50 Pa and a Permeability of 6.17 m3/h.m2. However, as I was less than halfway through the sealing process outlined above at that time, it may not have been too bad and, in addition, the thermal imaging also carried out showed up a number of weak points where I was losing heat such as hall door, hot press, fireplace/stove and attic door. I have subsequently dealt with all of these now apart from the attic door.

Extract fan in back door
Cold air (blue) around attic door
The reduction in electricity use has been achieved by means of a detailed audit of all appliances, and their usage, and systematically going about tackling each of them. Whenever I'm replacing an appliance I choose the most energy efficient option available - the most recent example of this being an amazing induction hob in my revamped kitchen. LED technology has advanced rapidly in recent years and I now have an LED option in almost every room which has more than halved my electricity usage for lighting in recent years. A dramatic reduction came in 2008 when I installed SOLARFOCUS solar panels for hot water and in the process did away with both summer electric immersion and electric power shower in one fell swoop - anyone used to a power shower might find my gravity fed shower a little tame but I find it more than adequate!

It may seem counter intuitive to be putting in electric heaters but the heat loss for the house is now so low (less than 3kW) that they are only needed to supplement the solid fuel stove I installed in 2006.  In addition, I am now generating my own electricity from my solar photovoltaic (PV) system (see my separate post on this for more detail and latest data) and, as I am exporting almost 80% of output to the grid, my net purchase of electricity is running at just over 500 units in a 12-month period at a net cost of about 200.  It seems to me very last century to pipe a fossil fuel halfway across Europe into my home to burn it in a boiler and then pump the hot water all around my house!

In December 2013, I replaced the existing solid fuel stove with a dedicated Charnwood C4 wood burning stove. I choose it for its clean-burn and air-wash technology designed specifically to re-ignite volatile by-products emitted by the initial burning. As wood is composed of 80% volatiles this is critical and I am amazed at how little ash is being produced which indicates to me that I am getting a very complete combustion. This series of stoves also features an integrated inlet for ducting external air to the combustion area rather than sucking it from the room and combined with the flue liner connected to it (rather than going straight into the chimney as with the old stove) I now have a closed airtight system.  Pat

Ready for Winter!

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