Winter's arrived in an energy efficient home, so what does this mean so far ?

Yes, it's December 2017 already and as reminded by the BBC weatherman, that's the beginning of 'meteorological winter' and it'll not be long 'till the festive season. Whether that brings thoughts of 'bah humbug' or welcomes in the advent countdown, it certainly means that the time that we'll all need to consume more energy than normal has arrived.

Three months ago heralded the beginning of autumn which sparked the idea for a couple of blog posts which, in the season of colour change, were intended to provide an idea of the level of energy consumption in an energy efficient household, not only electricity, but gas for heating too as it's important to not only focus on energy saving technologies such as solar photovoltaic systems and reductions in imported electricity consumption, but also include energy required to provide domestic hot water (DHW) or space heating. With this in mind, it'd probably be interesting to some if the information was updated on a regular basis, so let's take a quick peek at what energy usage can look like in an extremely energy efficient house over the past three months.

Electricity

Very much like many other homes, we use electricity - it's not really surprising considering that I'm writing this on a device powered by electricity as the form of energy has been around in abundance for quite some time, however, the difference is that although it's dark outside and there's currently a 50" TV, a laptop, some lights and all of the devices you'd normally expect to be consuming power in a modern home, we're currently drawing a mere 100W from the grid, little more than a single incandescent bulb of just a few years ago.

Power during daylight hours is mainly supplied by our solar PV system, which even at this time of year provides the majority of our daylight energy needs. The combined seasonal effect of shorter daylight hours on the solar pv generation and additional lighting/cooking/heating is apparent on the imported electricity consumption chart as a daily seasonal imbalance of approximately 2-3kWh on a total import requirement of around 1150kWh, which includes running a high efficiency air to air heat-pump, mainly in daylight hours. Of course, this can be bettered, but only when storage systems become available at realistic prices.

Gas

The home in question is insulated well above current UK building standards requirements and apart from the ubiquitous gas central heating, also has what would nominally be classified as secondary heat source in the form of a log-burner and a tertiary provision through a small heat-pump, although the majority of space heating provision is locally sourced biomass through the log-burner in order to minimise the carbon-cycle. Apart from this, there's also a significant heating provision provided be solar gain when the midday winter sun is closer to the horizon. A solar thermal system provides the vast majority of annual hot water requirements, however this is supplemented as required by a highly efficient condensing boiler on a 'top-up' basis as and when required.

The combination of heating sources results in an exceptionally low reliance on gas as a fuel source, which seriously reduces the house's carbon footprint. As can be seen from the gas consumption chart, usage of this form of fuel is extremely low on an annual basis and mainly confined to the winter period we're now entering, so January, February & March. Total annual usage in recent years is normally well below 1000kWh.

Logs / Biomass

As mentioned previously, the majority of the

heat provision in our home is via what many would consider to be the secondary heat source, a log burner. The house has considerable internal thermal mass within it's internal structure, which is excellent for regulating temperatures for reasonable periods, and high levels of insulation within the building envelope to keep heat in or out, all of which are good for keeping warm or cool.

The result of this is that once the structure is 'charged' with heat, it keeps warm. When heat is required it's normally provided within the living areas during the day and regulated by using internal doors as baffles, then allowed to flow through the remainder of the house overnight. Yes, it's crude, but it certainly works for us.

This year we needed to replace the old log store to ensure that our fuel burned efficiently and as cleanly as possible. What was our rained-on & slightly damp stack of logs is now undercover and well aired. The log store was designed & built in-house and has a fully loaded capacity of a little under three cubic metres, which matches both our historical average annual usage and a full tipped load from our usual log supplier.

Since installing the heat-pump both the burn frequency and burn hours of our main heat provider has reduced significantly. Unless there's an unusually cold spell this winter, it's likely that we'll continue the recent trend of using far less biomass - hopefully that's the case as we've not ordered a load of logs from the normal source this year and look to use what we already have leftover from last year.

The chimney was swept a while back, but the first use of the log-burner this year only happened last week on Nov 29, this being due to a number of consecutive dull & relatively cold days, since which it's had two more burns - all three being quite short, around 6 hours each time, so not even a basket-load of biomass consumed so far.

Autumn 2017 energy consumption update

So, as an update to the previous season entry, let's have a look at the energy usage over the autumn period in this energy efficient home.

For information, the logs aren't accurately weighed, but the energy used/provided is a reasonable estimate based on the burn time, type of fuel burned, and quantity used in terms of basket loads ...

Electricity kWh Gas kWh Logs kWh.t (est)

September 83 0 0

October 101 0 0

November 121 23 80

For Autumn 2017 as a whole compared to the previous year, electricity was fractionally higher (4.8%), with gas marginally lower (34.7%), and log usage being around half of what it was over the same period last year, however, due to the extremely low consumption in terms of energy, the year-on-year consistency is remarkably high considering the variables involved.