If you are planning any eco-building scheme, then you will place green energy somewhere near the top of your list. It is very easy to simply look at the descriptions issued by the manufacturers of renewable energy production systems, but how do you equate the figures with what you actually need? This is a question that I am frequently asked and there is no other way to answer it than to use …

…Simple Mathematics …  The following is simply an exercise in statistics and does not address the ethical issues of choosing energy supply, but all the same it is a task which must be tackled before any sustainable building can be successfully designed. For those of you who grow pale at the sight of calculations – then accept my apologies; but the concept is an essential element in good eco-design, and if need be, you ought to obtain balanced professional guidance.

Energy Units … You should calculate energy requirements by using units of energy – kilowatt hours in terms of time (kWh/day) – in other words the amount of power used over 24 hours. In the UK, the total amount of energy consumed * by each person is reckoned to average about 125 kWh/day, but this figure obviously covers all power usage. Depending on the source of information, it is estimated that the average UK home uses electrical power of between 3300 kWh/year (or just over 9 kWh/day) and 4700 kWh/year (about 13kWh/day). Northern Ireland’s domestic consumption for 2007 averaged 4400 kWh/year (12 kWh/day). Ireland’s consumption per capita is roughly equal to the UK. Check your electricity bills to see how you compare.

To give an example of how appliances measure up, if your home uses an average of 500 W (0.5 kW) then it will consume 12 kWh/day. If left switched on all day, an energy-efficient (11W) light bulb uses (0.011 x 24) = 0.264 kWh/day and a desktop computer using an average of 125W will consume (0.125 x 24) 3 kWh/day. It is not so simple to calculate the power consumption of some appliances just by checking out the wattage since power demands can fluctuate, e.g. fridges use power according to their ‘chill’ setting in relation to the ambient room temperature. Don’t forget that other non-electrical appliances such as stoves or oil burners also need to be included.

Renewable Energy … Renewable-power generating appliances need to be compared to see what they can achieve for you. Roof-mounted micro-wind turbines are probably not very effective in providing for your overall electrical needs. It has been estimated that a “600 W” micro-turbine mounted on a typical roof in England generates only 0.04 kWh per day – about 7 per cent of the power used by an 11 W light bulb.In contrast, roof-mounted solar water heaters make good sense. Even where the sunlight levels achieve only about 30 per cent, a 3-square-metre panel can supply on average about 3.8 kWh per day (i.e. perhaps half of a typical family’s hot water).

Other technologies are often viewed as ‘less green’, such as heat pumps; but if they drew power solely from renewable sources (i.e. wind farms, etc) then they would be a logical environmental choice. Some of the newer ones can deliver as much as 4.9 kWh of heat in the form of hot air or hot water, using 1kWh of electricity to do so.A final thought… before paying out money to provide energy, first put into action ways of reducing your power requirements.

Transition Omagh (google it if the name is new to you) are screening a free film on 'Gaslands Fracking' at Bogan's pub in Omagh at 8pm on the 1st of Feb - you are all very welcome (mine's a pale ale by the way). Come at 7pm if you would also like to hear what Transition can do for you ...

This is relevant to anyone with a site in the countryside which needs a septic tank (or package plant, etc).

Be aware that for the purposes of 'saving' the planning approval on a site by commencing works, some approvals will stipulate that "... consent to discharge effluent must be obtained before work commences...". This is an important pre-condition which must be met in order to comply with the commencement of work time limits.

For an application for consent to discharge effluent from a dwelling (i.e. for a septic tank on a rural site in NI) - the fees are now £100.00 for discharge to an underground stratum and £250.00 for discharge to a waterway. For the discharge to a waterway, that represents an increase of 127% over the old fee... !

Hi All,

I have recently been looking at insulation costs and doing a few sums.

Below are typical loft insulation costs from PowerNI (based on contractors 'provide & install' prices):

Flat                                           £385

Mid Terrace                             £323

End Terrace                            £303

Semi Bungalow                       £404

Detached Bungalow               £524

Semi Detached House           £327

Detached House                     £459

For the PowerNI Cashback offer, subtract £150 from the total.

There were no further details on how these costs were estimated so I tried this quick calculation for a DIY project: Take as an average sort of example a house with 125m² of loft space which is currently insulated with 100mm of glassfibre, so it will need another 170mm of insulation to bring it up to an acceptable standard.

B&Q are currently selling 170mm rolls of ‘Everyday Eco Loft’ insulation rolls at £3.12/roll. Each roll covers 5.5m² so for the 125m² loft you need 23 rolls, costing £71.76. If you can tackle this simple DIY or get a friend to do it, you could insulate this size of loft for less than £100.00, including your fuel costs to and from the store.

Even if the house had absolutely no loft insulation, a DIY 400mm installation (46 Knauf rolls from B&Q at £3.00 for a 200mm roll) would still only cost £138.00 !

There are plenty of other deals on insulation, so shopping around could get even better results.

Any questions or suggestions? Please post your comments below.

One last thing:

IF YOU ARE ELIGIBLE FOR FREE INSULATION - MAKE USE OF IT NOW!

Hi,

Would you like to read my latest article? Entitled ‘Lay of the Land’ and published in the Autumn 2011 issue of Selfbuild magazine, it discusses the importance of soil when choosing a site. There’s more to it than you might think!

You can also read it online at www.selfbuild.ie

All feedback welcome.

Thanks,

Les.

In our PowerNI BIG Energy Saving Challenge, I have been collecting data on our households' energy usage. One little difficulty that has arisen is how to quantify and place a cost / value on firewood.

Bags seem to be the standard unit of sale for firewood - but I have also been seeing pallet and trailer loads advertised - so it can be difficult to apply a suitable standard unit. The other thing is that hardwoods will generally be heavier than softwoods (but not always) - and there is a difference in the amount of heat that the two types can generate. Moisture content also affects both heat output and weight.

For now though, I will use cubic metres - and just need to know the average weight.

Question: How much of your firewood in terms of weight does it take to fill an ordinary 25kg coal or bag?

Please post your comments below.

Thanks,

Les.

HOT WATER TAPS

Traditional screw head water taps are found in most dwellings but they waste energy when hot water is run for longer than necessary; i.e. the tap is not always turned off as soon as it could be, so unused hot water runs out of the plug hole. If we replace our screw tap with a push on / self closing tap how much could we save in terms of energy costs?

The average screw head tap will deliver approx 12 ltrs per minute when turned partially on. On average a screw head tap is left on for 15 seconds. Assuming each person on average washes their hands 4 times per day, this equates to 12 ltrs per day per person. On average the self-closing taps will reduce this to 6 ltrs per day because the flow rate of a selectable flow rate push tap can be adjusted to run from 4 ltrs per minute and the time on can be reduced to between 3 and 11 seconds.  The push tap cannot be left running, as it self closes.

Over the period of one year, for a family of 4, the total hot water used at one tap to wash hands is 17,520 litres for a normal screw tap and 8,760 litres for a push tap.

Irregardless of the temperature at the tap* (recommended maximum of 41⁰C), water should be stored at temperatures under 20⁰C or above 60⁰C. I reckon that the average temperature of water in my cold water tank is about 10⁰C.

Here are the sums:

Screw Tap: Heating 17520 litres of water from 10⁰C to 60⁰C (using electricity at 17.8p/unit) will cost:

17520 kg x 4186 J/kg⁰C x 50⁰C / 3.6MJ x £0.178 = £181.31

Push Tap: Heating 8760 litres of water from 10⁰C to 60⁰C (using electricity at 17.8p/unit) will cost:

8760 kg x 4186 J/kg⁰C x 50⁰C / 3.6MJ x £0.178 = £90.65

Payback: A push tap at £32.00 fitted using DIY (so zero fitting cost) gives a payback time of £32.00 / (£90.65 / 365) = 129 days or about 18½ weeks

Any questions or thoughts? Please post a comment.

* A mixer tap or hot and cold taps provide water at the correct temperature in the sink, bath, shower, etc.

As we all know, before installing expensive renewable energy sources in our homes – we must make it as energy efficient as possible first. As heating forms a large part of our energy usage, it is useful to know where we are losing heat – and the best way to do this is to get a thermal imaging survey done, preferably before and after the insulation and air-sealing work to your dwelling. The ‘before’ images will show where you need to make improvements and the ‘after’ images will show what you missed!

This photograph gives you an idea of what the survey can show you.

A typical thermal image of a block of flats constructed to the PassivHaus standard (right) versus a more traditionally built design (left).

Dwellings constructed to PassivHaus standards can have space heating energy requirement up to 90% less than existing building stock.

(Image courtesy of PassivHaus Institut Darmstadt.)

Hi folks,

I should have published this earlier - sorry!

You can also check out our group's progress in the Big Energy Saving Challenge on the PowerNI website.

Also - if you would like to receive regular news and details about forthcoming events - let us know here.

Have a good weekend,

Les.

Hi All,

One of the first things that you will need to do when starting your energy saving project for real - is to carry out your own energy saving check (HEC). You can find this on the PowerNI website and it doesn't take long to do - just click the 'HEC' link below to get started:

HEC

When you have your data collected - you can re-visit it at any time to make improvements, follow the advice, remind yourself on what to do next, etc...

'Bye for now,

Les O'Donnell.