RefurbN16

Tag: Heating

  • Solar Thermal Systems – Part 1

    A couple of weekends ago a group of us went to see a very interesting solar thermal installation in Stoke Newington. Generally, solar thermal systems supply heat for hot water only, but this system did a lot more than that as it was also plumbed into the heating system.

    I’ll go into more detail on this particular system in a second post later this week, but first up we have a little overview of solar thermal technology…

    Solar water heating systems are the most common form of microgeneration (small scale renewable) technology in the UK and Europe. This technology has been around for quite a long time (since the 1970s in this country), quietly generating heat in sunny weather to make a significant contribution to a home’s hot water energy consumption.

    Naturally they perform best in the sunniest summer months, when virtually all of your hot water needs can be supplied by a good quality installation. Even during the winter months, a sunny day can result in a substantial amount of hot water being generated.

    It is worth noting at this point that hot water energy consumption comprises around a quarter of a typical home’s total energy needs. Space heating uses the lion’s share, making up nearly 60% of total consumption. So a solar thermal system that only supplies hot water won’t cut your total energy consumption drastically, but it does make a good contribution.

    Harnessing heat from the sun is, in essence, very simple: a collector is mounted on a south facing roof, absorbing the heat from the sun’s rays. The collector has a network of pipes through which a fluid passes, warms up and then takes the heat to a water-filled cylinder for storage and later use. There are two types of collector: flat plate and evacuated tube.

    A flat plate collector is the simpler of the two, consisting of a glass covered heat absorber with pipework passing through it. This type of collector is the cheaper of the two, but it is also less efficient so harnesses less heat for a given area of collector.

    Evacuated tube collectors consist of an array of glass tubes with copper strips running along the middle. The glass tubes have had the air removed from them which reduces losses due to convection and conduction and allows them to reach higher temperatures than flat plate collectors. This means that they offer better performance, absorbing more heat for a given area of panel,  but they do cost a bit more.

    The fluid passing through the collector is usually water mixed with a form of antifreeze, along with a chemical that reduces corrosion. This fluid is kept completely separate from the hot water that comes out of your taps.

    Apart from the collector, you’ll also need somewhere to store all of this lovely heat and a conventional hot water cylinder won’t be enough.

    The most common solution is  to fit a twin-coil cylinder which has one coil in the lower part of the cylinder fed from the solar water heating and a second coil in the upper half of the cylinder which is fed from the boiler. The solar thermal system therefore supplies as much heat to the water as it can when the sun is out and then the boiler tops it up with additional heat as necessary.

    This need to store heat means that combining solar water heating with an combination boiler can be tricky (although it is possible) because the space for a decent size cylinder will most likely have been given up for other purposes. If you are ever considering removing your hot water cylinder and opting for a combination boiler, consider whether you might want to fit solar thermal at a later date.

    As ever, when considering microgeneration technologies make sure that you’ve gone as far as reasonably possible in terms of reducing your energy demand first. Ideally you should reduce demand as far as possible before considering generating because for the most part it is much more cost effective to reduce energy consumption than it is to generate.

    The Energy Saving Trust has a good publication on solar water heating which gives a more detailed overview of the technology, but it only goes as far as using solar thermal for water heating. The system we saw was also plumbed into the heating system, allowing the user to make use of much more of the heat falling on the roof.

    A system that just heats the hot water can only go so far because you only use so much hot water (unless of course you are particularly partial to baths). If you have lots of sunny weather the panel will keep generating heat and that heat has to go somewhere. Being able to deliver it to radiators or an underfloor heating system is a real bonus.

    I’ll post more details about this fully integrated system later this week.

  • Sustainable Refurbishment – Towards an 80% Reduction in CO2 Emissions

    The UK’s building regulations didn’t start to consider energy consumption until the 1960s, when very basic requirements to conserve energy were placed on house builders. These requirements have slowly been tightened over the decades and the introduction of the Code for Sustainable Homes has accelerated this in recent years.

    The intention is that new build homes built from 2016 will be zero carbon (although the exact definition of ‘zero carbon’ in this case is still up for grabs). The problem is that the UK’s housing stock is the oldest in the developed world, with 8.5 million properties over 60 years old and an estimated 24 million homes built up to 2016 expected to still exist in 2050.

    Zero carbon new build homes are definitely needed so that new homes don’t add to emissions, but all of the carbon reductions will have to happen in homes that have already been built.

    In the previous post we looked generally at a whole house approach to sustainable refurbishment. The Energy Saving Trust has recently published an interesting new publication which looks at this in more detail and points the way towards an 80% reduction in CO2 emissions in existing homes. This guide is aimed at homeowners as well as housing developers and builders and is clearly written and nicely presented.

    It gives an excellent overview of the energy efficiency measures that can be implemented in the UK’s homes including the different types of wall, roof and floor insulation, improving windows and doors, increasing air tightness as well as efficient heating and hot water systems and lighting and appliances. Also covered are microgeneration, water efficiency, waste and recycling and even climate change adaptation.

    If you want to get a good picture of what needs to be done to our homes, then this is a good starting point. Hopefully it will stimulate you to consider which of these measures can be applied in your home.

    The Energy Saving Trust has lots of interesting technical guidance. More information can be found here.

  • Curtains and Radiators

    This topic came up tonight: what do you do with a curtain hanging over a radiator? And why are radiators sited under windows anyway?

    Back in the day, radiators were located under windows for a counterintuitive, but valid reason, although it has more to do with comfort than energy efficiency.

    Imagine a room with single glazing and a radiator on the opposite wall. The air beside the window will be cooled and will sink as it becomes denser. At the opposite end of the room the air is warmed by the radiator and will therefore rise.

    These two effects combine to circulate the air around the room, but this circulation will draw cold air from the window down into the centre of the room where you are sitting.

    Stick the radiator under the window and it will warm the air beside the window, causing it to rise into the room. At the other end of the room it will descend, but it should be at a warmer, more comfortable temperature. It’s worth noting that with double glazing, this isn’t really a problem and you can locate your radiator wherever is most convenient.

    So radiators are usually found under windows which have curtains which, more often than not, hang down below the top of the radiator.

    Having them hang in front of the radiator is a big no no. All that lovely heat will rise up behind the curtain, right against the single glazing and will be trapped there before leaking out to warm the outside air.

    Tucking them behind the radiator can also be counterproductive. Radiators work best when they have a free and unobstructed flow of air around them, helping to set up the convection* currents that circulate warm air around the room. For this reason you definitely want to avoid radiator shelves and radiator cabinets.

    If you take a look at a typical radiator, you’ll see there are the thick bits through which the hot water flows, and thinner fins that transfer the heat to the air. It’s these fins that you need to keep clear and unobstructed, and tucking a curtain around them will reduce their effectiveness.

    So what’s the solution? Cut the curtains so that they hang a bit above the radiator and then find some way of holding them flush against the wall. Hooks? Velcro? Elastic? Whatever works best. Just make sure that as little hot air as possible escapes behind the curtain and as much air as possible can flow around the radiators.

    By holding the curtain flush against the wall, you will not only prevent warm air from rising behind the curtain, but you’ll also trap a layer of air there. Air is a fantastic insulator, as long as it is kept still, so if you can keep the air between the curtain and window  as motionless as possible, you’re on to a winner.

    * radiators are really badly named – they’re convectors, not radiators; but radiators they shall be known as for ever and ever…

  • Boilers Pt 3 – Boiler Brands

    Replacing your boiler is an expensive undertaking and it’s not hard to find stories of boilers dying in fairly short order.

    Like most things in life, you get what you paid for and boilers are no exception. Cheaper brands are likely to use cheaper components that are more prone to malfunctioning and can easily cost you more in the long run.

    But if you buy a good quality condensing boiler and it’s installed and maintained well, there’s no fundamental reason why it shouldn’t have a long life of delivering substantial energy savings. But which boiler brand is best?

    There aren’t any scientific comparisons, but the excellent consumer magazine Which? ran a survey (sub required but you can get a one month trial for £1) amongst 3,000 of their members who had purchased condensing boilers since 2005, rating customer satisfaction.

    The survey found the highest customer satisfaction came from Vaillant and Worcester Bosch customers. Runners up were Vokera, Potterton, Glow-worm and Baxi.

    The boiler scrappage scheme is currently underway, offering £400 for the replacement of a G-rated boiler with a new A-rated condensing boiler. You can find out if your boiler qualifies by checking here.

  • Heating Controls Pt 2 – Programmer and Room Thermostat

    This one often causes vigorous disagreements, but I’m going to stick my oar in and describe how I think the programmer and room thermostat (see Pt 1 for a description of these controls) should be set in a home.

    The very quick version is:

    1) Work out what the minimum comfortable room thermostat setting for your home is and then

    2) Set the heating to come on for as little time as possible

    It sounds simple but there are some subtleties to it that I’ll discuss now. Unfortunately there isn’t a great deal of hard research to go on. This is my best guess and I’m happy to hear contrary views. If anyone can dig up proper research, I’d appreciate it.

    Now first up, there is some evidence to suggest that if the fabric of the house is cold then you need to heat the air to a higher temperature in order to feel warm. The thinking goes that the additional radiated heat from the walls makes a difference to comfort and as a result, if you let the walls warm up you can get away with a lower air temperature.

    This is borne out by plenty of anecdotal tales of people changing from bimodal heating (having it on twice a day) to continuous heating but setting the room thermostat to a lower temperature and reporting energy savings while still being comfortable.

    Unfortunately it’s very difficult to compare two different heating patterns because your home’s energy consumption is so dependent on the outside air temperature (it is possible though by taking regular meter readings and doing a degree day analysis, but that’s for another time).

    Turning your thermostat down does lead to substantial savings. Everything else being equal, heating consumption is cut by about 10% per degree you turn it down. But having your heating on all the time? I’m certain that’s not efficient because you’re heating the home when you’re fast asleep or out of the house and I’m sure you could at least shut it down for a few hours in the middle of the day or night.

    If your home is not very responsive (i.e. it takes a long time to heat up), which many solid wall homes are, it might take a long time to heat up the walls and so it might seem like you’re ignoring the second part of the above advice.  might mean that you need to have the heating on for quite a while in order to get the fabric of your home up to temperature.

    So here is my patent pending method for setting your heating programmer and room thermostat:

    A bit of experimentation is called for…

    Stick your heating on for a good length of time on a reasonably chilly day and let the fabric of your house completely warm up and stabilise at a higher than usual temperature. Then start lowering the room thermostat until you get to the lowest temperature at which you are still comfortable. Depending on your home it may take a little while to let the temperature adjust.

    Next turn your heating system off and note how long it takes to cool down enough so that you’re starting to feel a wee bit nippy. This is your home’s cooling down time, we’ll call it C. When your home’s cooled down completely, turn it back on and work out how long it takes to get back up to the comfortable temperature. This is the warming up time, W.

    You then want to set your heating so that it comes on W minutes before you wake up in the morning and switches off C minutes before you leave the house. Set it to do the same before you get home in the evening / go to bed.

    If you have it on any longer than this, you’re heating your home unnecessarily, but do bear in mind that it might take a while to get the fabric of the house up to the right temperature.

    Does that make sense? It’s not an exact science but this is the best I’ve been able to come up with. As I said, comments gratefully received!

  • Boilers Pt 2 – Condensing Boilers

    In Boilers Pt 1 – Regular Vs Combi, we looked at the two main types of boiler which you find in the home. This post takes a look at replacement boilers, in particular condensing boilers.

    Since 2005, the Building Regulations have required that if you replace your boiler, you have to replace it with a condensing boiler. There are a few exceptions to this (see Appendix A here), but essentially all new boilers condense. But what does this mean?

    A condensing boiler is not all that different to your old boiler, but it is more efficient. To achieve this, condensing boilers are fitted with an extra heat exchanger. The heat exchanger transfers heat from the burning gas in your boiler to the water in your heating or hot water system.

    A heat exchanger is a very simple metal component through which water is passed. It has a large surface area which makes it easier for the heat to pass from the hot burning gases to the cooler water in the heating or hot water system. A radiator is an example of a heat exchanger, passing heat from the hot water to the air in your home.

    By adding an extra heat exchanger to the boiler, more heat can be extracted from the hot gases that would otherwise escape up the flue and into the atmosphere. This energy goes into preheating the water returning from the heating or hot water system, before it passes to the main heat exchanger to be heated up the rest of the way.

    The “condensing” part refers to the moisture (or “condensate”) which condenses out of the gases and is flushed down the drain. The action of condensation transfers additional heat to the heat exchanger (see here for the Wikipedia explanation).

    Condensing boilers reduce the temperature of the flue gases from about 150°C to about 55°C so there is a substantial amount of heat there to be recovered but they won’t always be in condensing mode. In order for this to happen, the temperature of the return pipework (which carries the water back to the boiler after passing through the radiators) has to be below 55 degrees.

    For this reason you need to make sure that a regular boiler is correctly sized for your home. This is one of the reasons why you should reduce the heat demand of your home as much as possible through insulation and draught proofing before replacing your boiler. If you do it the other way round, your boiler is likely to be too big and it won’t work as efficiently.

    Your boiler thermostat also needs to be adjusted so that the flow temperature (the temperature of the water leaving the boiler) isn’t so high that the return temperature is too high for the boiler to enter condensing mode. I’ll cover this in more detail soon.

  • Boilers Pt 1 – Regular Vs Combi

    Existing boilers in UK homes fall into two main types – regular boilers (which might also be called “heat only” or in some cases “system” boilers) and combination or “combi” boilers.

    A regular boiler delivers heat to both the heating system (usually radiators) and a separate hot water system which takes heat to the hot water cylinder. A hot water cylinder consists of a metal tank, hopefully well insulated, inside of which is a coil of tubing. The boiler passes hot water through this tube and this indirectly heats the water in the cylinder.

    So instead of taking the water to the boiler you take the heat to the cylinder. When you turn on the hot tap, hot water is taken from the top of the tank and replaced with cold water at the bottom.

    A combi boiler on the other hand, supplies heat directly to both the radiators and to the cold mains water so it directly heats the water itself and delivers it on demand to the hot taps. Combi boilers store no water and so they avoid the problem of sometimes heating up water that  just sits there cooling down (known as standing losses).

    Now you may be thinking “why bother with a regular boiler and hot water cylinder if you can avoid those losses?”, but there’s a catch with combis: they heat water less efficiently than regular boilers. So there’s a trade off between the benefit from avoiding standing losses and the penalty from reduced hot water efficiency.

    The upshot of all this is that a combi is most suitable for smaller homes with a low hot water demand while a regular boiler is most suitable for a home with high hot water demand. Combis are also more suitable in smaller homes because they don’t need the space for a cylinder.

    In my flat I unfortunately have a cylinder which means that I don’t use anywhere near the full amount of hot water. But it is very well insulated with factory fitted foam which means that I just have it come on once before I get up and there’ll still be hot, well warm, water when I get back in the evening.

    There is a trend at the moment towards the inappropriate replacement of regular boilers with combis but it should be resisted. If anything, removing the cylinder makes it that little bit harder and more expensive to install a solar hot water system, which needs as much storage capacity as possible, so if you’re considering going down this route you should try and keep hold of your cylinder.

    Next up we’ll cover high efficiency condensing boilers. If you want to read in more detail about gas heating systems then your best bet is to check out the Energy Saving Trust publication Domestic heating by gas: boiler systems (CE30)

  • Heating Controls Pt 1 – Introduction

    Given that it’s bloomin’ freezing outside, I thought I’d write the first post on setting your heating controls.  This post will be an overview to the whole set of controls and it’ll take a few more posts to cover the whole lot.  For many this is a confusing subject so hopefully this post will help shed some light on a difficult area.

    Ideally your heating system should have at least 3 basic controls: a boiler thermostat, a room thermostat and a programmer. We’ll deal with them in reverse order.

    The programmer has overall control over when the boiler is switched on and off. It doesn’t have any temperature setting, just time settings. They come in varying degrees of sophistication from the most basic (which I unfortunately have) which can’t control the hot water and heating independently, to all singing and dancing, fully programmable digital devices. If the programmer is set to on, it doesn’t mean the boiler will be chugging away all of the time – the boiler should kick in and out in order to maintain a comfortable room temperature.

    This overall house temperature is set by the room thermostat, which is usually found in the hallway or living room of a home. It senses the temperature of the room and tells the boiler to switch on if it is below the set temperature and switch off if it rises above it. As a result your room temperature will bobble up and down slightly above and below the set temperature. The room thermostat can’t override the programmer so it will only have an effect if the programmer is in its on phase.

    The boiler thermostat is mounted on the boiler and controls the temperature of the water flowing out of the boiler and into the pipework and radiators. It tells the boiler how long to burn for in order to raise the water to the set temperature.This control is frequently overlooked and is usually the least well understood thanks to generally poor design.

    In an ideal world, all of these three controls will work together in perfect harmony to maintain the temperature of your home. By setting them correctly you can achieve this with minimum energy consumption.

    Clear? As mud? Post a comment below if you want me to clarify anything. I’ll be going into more detail on this very soon.

  • Boiler Scrappage Scheme Launched Today

    The other big news today was the launch of the boiler scrappage scheme by the Department for Energy and Climate Change (DECC). The full details of the scheme can be found here, but here is the 30 second version…

    The scheme is offering 125,000 homes a £400 voucher on a first come, first served basis if they scrap their G rated boiler and replace it with an A rated condensing boiler. Condensing boilers are more efficient than conventional boilers because they extract additional heat out of the exhaust flue that would otherwise escape into the air.  They shouldn’t be confused with combination (combi) boilers which are boilers which don’t have a hot water tank, heating the water directly instead.

    The building regulations require (with a few exceptions) at least a B rated boiler to be fitted so this is pushing the bar a little higher, which is a good thing.

    The way it works is that once you’ve identified your G rated boiler and have received a quote that you’re happy with, you contact the Energy Saving Trust. From January 18th, cashback vouchers will be sent out and you should receive the voucher about 10 days after application. You then have 12 weeks to have the boiler installed and the voucher signed off by the plumber.

    A word of caution… You might well be quoted wildly different figures, some of them way too high (naming no names of course), so make sure you get a good selection of quotes. If you can find a good local plumber recommended by word of mouth, that might be the best way. Just be aware! There’s also a wide range of boilers. Some are cheap but poorly constructed and with expensive parts.

    You can find out if your boiler is G rated here. If you’re having difficulty, post a comment and I’ll see if I can find it (it’s not always completely obvious).

    Now while this is a good offer (it’s equivalent to a discount of about 15% to 25%), it’s really best to consider reducing your energy demand before you replace your heating system. This will mean that the boiler can be correctly sized to the heat demand of the home. Having said that, this is a one-off offer and is highly unlikely to be repeated.