Saturday, 4 November 2017

How is a thermal store different from a hot water tank?

People often ask if they can use heat from their solar panels for heating as well as hot water. The short answer is no, because the solar panels heat your hot water tank which supplies hot water to your taps, not your radiators. The long answer is you could, if you installed a thermal store instead of a hot water tank, though this may or may not be a good idea. A thermal store is also a big tank of water it works in a different way so it can be used for space heating as well as hot water. Thermal stores can be useful in various situations:
  • You can combine heat from different sources, e.g. solar panels or a wood stove as well as your boiler
  • You can store heat to optimise use of your heating system - for example if it is inefficient to turn on and off according to demand (particularly useful for log burners but also for other biomass boilers or even heat pumps).
  • It can store heat when power is cheap for use when it is expensive. For example, using a thermal store you can avoid running your heat pump at peak times and get a cheaper tariff (at least you will when we all have smart meters and time of use tariffs are available).
The size you need depends on what you want to do with it.

Wednesday, 25 October 2017

What will smart heating controls do for me?

People interact with their heating controls in different ways. Some people leave it how the engineer set it and dare not touch, others use the thermostat as an on-off switch; some want a set-up and forget system with only occasional need for twiddling, still others would really like something that is clairvoyant and does the best thing without them having to do anything at all. Most people agree that it isn't an easy subject. Can smart controls help? In fact what are smart controls?

Heating controls was the subject of half my Cosy Cambridge workshop on Monday. With the help of some friends we managed to cover all the basics and had a good discussion on whether 'smart' controls were a good idea, or rather under what circumstances you would benefit. You can download the slides from my website here.

Sunday, 22 October 2017

How much less water do modern houses use

Cambridge is growing and more people means more water consumption, which is a concern in this area. Will the new homes use as much water as existing ones? Building regulations require that new homes are fitted with water efficient appliances so that an 'average' person will use no more than 125 litres/person/day (lpd). This is considerably less than the UK average 141 lpd. So what is an 'average' person? Using the water calculator specified in building regulations I have estimated water consumption for this mythical individual using water efficient appliances versus a traditional context - by which I mean one from a few decades ago. Based on this estimate, even if all new homes use the most efficient appliances that would not be enough to keep Cambridge's usage within the allowed limits.

Here are the headline figures: the efficient house comes in at 104 lpd compared to 146 for the traditional house, and 47% of the difference is due to savings from flushing the WC. This chart compares the two.
Total use Efficient home 104 lpd, Traditional 146 lpd. For assumptions and use factors see below.

You might like to compare your usage with the 'average' person. If you use more then you could probably save more too.

Thursday, 12 October 2017

Can smart meters give us energy saving advice?

Would you like a smart meter that told you how much you can save by turning down your heating?  Current smart meters can't do this but researchers at the University of Bath reckon that it should be possible, with the aid of some extra sensors for temperatures and CO2 levels. They devised a system which could give you prompts such as 'We have noticed your thermostat is set to 23C. If you reduced the thermostat to 21°C you would save 11 kWh; this is equivalent to £1.43.'  (I think this must be per day and using electricity) [1]. They found that residents in their experiment were very likely to follow this advice. But all these extra sensors will be expensive - can we manage with less?

Wednesday, 4 October 2017

Recycling solar panels and PVCu windows

Over the years I have installed PVCu¹ windows to save energy (but actually mainly just to be warm) and solar panels for renewable energy - what will happen when they get old and have to be replaced? The way that we deal with materials at end of life can make a significant difference to the overall carbon savings. For example both panels and windows contain glass and other materials that take a lot of energy in manufacture. If they are recycled properly and reduce emissions from building the next thing, then the overall carbon emissions can be significantly reduced. Does this happen?

There are two issues with recycling that are slightly related:
  1. What is possible? How much material can be reused or recycled and how much energy can be saved by doing so?
  2. Does it happen? Is there a recycling supply chain that actually picks up most of the waste generated?

It turns out that for windows and for solar panels high levels of recycling are achievable. However, whether this actually happens or not is another question.

Monday, 2 October 2017

How to ramp up energy efficiency without subsidies

There are many things we can do to save energy at home but some of them take so long to pay back we can't afford to think that far ahead. If you factor in other benefits such as reduced carbon emissions and improved air quality that benefit society as a whole, then the finances look much better. But those costs (often called social costs) are not included in our energy bills and we would be very unhappy if they were, at least without some other compensation. Adding in the carbon cost to my gas bill would mean an increase of 25%! [1] We need a way of adding these costs to our bills without leaving us out of pocket. Maybe we need something like the Carbon Fee and Dividend. This would make a great deal more energy efficiency savings financially viable for households and businesses without subsidy.

Friday, 22 September 2017

Why I haven't installed a heat pump (yet)

If you read this blog you will know I am keen to promote heat pumps as a low carbon heating technology, so I feel a bit of a hypocrite not having one at home. Since we have insulated our house as much as we can it is a logical next step to a low carbon house. So I made enquiries with two heat pump installers - but no joy. This blog post is a personal story. Every house is different and doubtless you won't meet exactly the same issues, perhaps even none of them.