Biomass Heating. The Basics. Tel Rev 6 August 2013 P a g e 1

Transcription

1 Biomass Heating The Basics Tel Rev 6 August 2013 P a g e 1

2 Summary This guide will attempt to explain in simple terms the benefits of a Biomass heating system both financially and environmentally. Homes using Biomass technology can reduce their carbon footprint, save money reduce bills and earn money through the Renewable Heat Incentive (RHI) Contents Page Introduction 3 What is Wood Fuel? 3 Surely Burning Trees Can t Help The Environment? 3 What Needs to Be Considered? 4 Space 4 Sustainability of Wood Supplies 4 Cost 4 What Types of wood Fuels Are Available? 5 Wood Chips 5 Logs 5 Wood Pellets 6 Fuel Quality 7 Fuelling Wood Boilers 8 Wood Chip Boilers 8 Log Boilers 8 Wood Pellet Boilers 8 Buffer Stores 9 Maintenance 9 Hot Water Demand 9 Help With Capital Costs 10 Renewable Heat Incentive (RHI) 10 Tel Rev 6 August 2013 P a g e 2

3 Introduction This guide describes how wood fuel can be used to supply heating and hot water in your home. It will help with assessment of the buildings suitability for this technology and gives a list of other considerations as a possible project is developed. Using biomass wood fuel heating can help families reduce their costs, increase the amount of heat available, at the same time reducing fuel costs and even earn additional income through the Governments Renewable Heat Incentive Scheme (RHI) What is Wood Fuel? Burning Wood Releases heat which can be used to heat buildings and provide hot water. It is the most common form of renewable heating in the UK with a million tonnes of wood being used per year, mostly on log fires and wood burning stoves. However, there are now a range of wood burning boiler systems that can be used to run central heating and hot water systems both in commercial and domestic applications. These are generally referred to as Biomass boilers. Biomass fuels are wide ranging but the most common one is wood in the form of logs, pellets or chips. Surely Burning Trees Can t Help The Environment? Burning wood does release CO 2, which is the greenhouse gas being blamed for global warming. The reason that wood is almost carbon neutral is that an equal amount of CO 2 was absorbed by the tree when it was growing. Sustainable forests are being grown all over the UK to provide the wood for Biomass boilers. The trees in these forests are absorbing CO 2 which will then be released at a later date. The problem with fossil fuels is that the carbon in them was absorbed millions of years ago and burning them increases CO 2 levels. Biomass wood fuel is not completely carbon neutral as there are some CO 2 emissions associated with the production and transport. For example a large retail facility may burn 8000 litres of oil per year which would produce around 25 Tonnes of CO 2. A Biomass boiler producing the same heat output would burn 4 tonnes of wood pellets but the CO 2 would only be 675kg. The main reason that Governments around the world are encouraging the use of wood fired heating systems is because of their commitments to reduce CO 2 levels. Tel Rev 6 August 2013 P a g e 3

4 What Needs To Be Considered? Space Biomass boilers generate heat in the same way as standard gas or oil fired boilers and therefore can be used in the same way using existing hot water cylinders and heat emitters such as radiators. If you currently have electric heating there will an additional cost for the supply and fitting of radiators and the necessary pipe work. (electricity is the most expensive form of heating so any costs will be quickly recovered with the savings made). Biomass boilers do tend to be bigger than gas or oil boilers due to their larger combustion chambers. These boilers work most efficiently when they run on maximum power and the best way to achieve the best efficiencies is to put the heat generated into a large water filled vessel known as a thermal store. Thermal stores take up a lot of room. Additionally, wood has a lower energy content per volume than traditional fossil fuels, meaning that the volume of wood to be burned will be much greater than the equivalent volume of oil. There will need to be sufficient space for the wood fuel to be stored. This storage area needs to be dry and easily accessible for delivery vehicles. Sustainability of Wood Supplies The environmental benefits of using wood fuel are clearly greater if the wood is sourced from a sustainable local supplier. All managed woodlands in the UK are required to have a licence issued by the Forestry Commission. As the market for wood fuel grows the number of suppliers will also grow creating competition in the market place which should help to regulate price increases. Gillies Gas Renewables will assist our customers in sourcing wood fuel. Cost Biomass heating systems have a higher capital cost than equivalent traditional fuelled boilers. This could be challenging in terms of raising initial funding. However, over the lifetime of a Biomass Heating system at least 70% of the cost is the fuel supply. Wood is generally cheaper than fossil fuel rivals, so while the initial capital investment is higher there are significant savings in the long term. Government funded RHI payments make a significant difference to a biomass project feasibility. Tel Rev 6 August 2013 P a g e 4

5 What Types of Wood Fuels are available? Wood Chips Wood chips can be made from virtually any kind of woody biomass including whole trees. They are made by a special chipping machine. Like pellets, wood chips are typically used in automated systems which makes them a clean and convenient heating option for both households and larger buildings including schools and hospitals. Woodchip is a cost effective, low carbon fuel, but it does have a low bulk density. Woodchip is likely to have a bulk density of kg/m3 dependent on the species and quality of chip. This means that woodchip requires a big storage space. This has an effect on storage and delivery costs of this material and is an important reason to source local fuel. If the large storage volume required for chip is likely to be a problem, wood pellets should be considered. Wood Chip is more convenient than Logs, as the boiler can be automatically filled, rather than having to load logs by hand There are two main sizes of wood chip used in biomass boilers G30 (max 3cm diameter) and G50 (max 5cm diameter) - you can either buy in chip to the correct standard, or you can hire a chipper to chip your own wood. The moisture content of chip is also very Important -most boilers are rated at a maximum of 25% moisture content. This is because the more water contained in the wood, the lower the heating value is, since water vaporises during the process of combustion. In doing so, heat will be consumed - decreasing the efficiency of the boiler, and potentially increasing corrosion of internal mechanisms. The only feed mechanism for wood chip is an auger (screw mechanism) attached to an agitator (rotating spring leaf) - so the boiler and fuel store need to be sited close together. Logs Logs are used in the most basic form of biomass boiler. These boilers are relatively cost effective to install, but the obvious disadvantage is that they will need to be filled up at least once a day. Logs for these boilers should ideally be well seasoned, as you would expect for a traditional log stove or fire. Logs do not come from chopped trees only. They can be also produced from coppicing, pruning and forest thinning, and do not cause any habitat destruction. Plantation wood is rarely used for wood fuel. Log heating systems such as log stoves and log boilers are suitable for some businesses but they require frequent manual refilling which makes them less convenient than other types of wood fuel such as wood chips and pellets that are mostly used in automated systems. Just about any tree species can be used for wood fuel but there is a major difference in energy output between different types of wood. For example, softwoods such as pine are less energy efficient than hardwoods such as oak which means that larger quantities of softwood are needed to produce equivalent amount of heat than hardwoods. For that reason softwoods are usually used during spring and autumn when less energy output is needed or in smaller quantities in combination Tel Rev 6 August 2013 P a g e 5

6 with hardwoods. In order to reduce the number of loading times on a log boiler it is normal to specify a larger boiler and thermal store than would normally be used with wood chip or pellet. Theoretically, you can choose between seasoned and unseasoned logs but energy and cost efficient use of wood fuel requires well seasoned logs. Unseasoned logs contain a significantly greater amount of moisture and do not generate as much heat as seasoned logs. In addition, they release larger amount of condensates that can build up in the flue system and cause serious damage. For that reason it is recommended to choose well seasoned logs that have been well dried. Log boilers cost the least from an installation perspective, as there is no feed mechanism required for the fuel although the larger thermal store will add some cost. A log boiler is a commitment in terms of the time required to manually load the boiler and careful thought is required about the implications. The main consideration for logs is the source - you don t want to run out. You can buy in logs, but the type of wood (hard/soft) and water content will vary log fired boilers are best suited for those with their own managed woodland. As a guide, a building using 12,000 litres of oil then would require a 120kW log boiler which would consume around 96m3 of stacked, split logs per year. This also highlights the need for sufficient storage space - you will need enough space for this heating season, and the next. Water content Heating value Fresh from the forest 50-60% 2 kwh/kg Stored over the summer 25-25% 3-4 kwh/kg Stored over a few years 15-25% 4 kwh/kg A log boiler, ideally should only be fired once a day It is not practical to have to keep feeding logs in all day. This means that you need a greater amount of thermal storage than you would for a pellet or chip boiler. And that the boiler will need to be a bigger size too - so that it can generate more heat in one go. Pellets Pellets are relatively new in the UK but they have been used in Central Europe and North America for some time. They are produced from wood by-products such as sawdust and wood chips. They are the most convenient form of wood heating because most types of pellet boilers are automated and require refilling once every few days only. In Europe, all pellets have to be uniform in shape and density, and contain less than 10% of moisture. They also must not contain any recycled wood or contaminants. The wood material is held together by lignin, a natural glue that is activated by heat when wood material is put under the press. Tel Rev 6 August 2013 P a g e 6

7 Pellets have several other advantages over logs other than convenience including high energy output due to low content of water and high density, lower volume to store, less ash and fewer deliveries required. Pellets are just as cost efficient as logs due to higher energy content but pellet boilers are more expensive than log boilers. Production of pellets is usually carried out within large production facilities producing tens of thousands of tonnes of pellets a year. A number of these plants are now up and running in the UK. Numbers of these plants are growing all the time and most customers in Scotland will have a plant within reasonable distance. Wood pellets take up less space than other forms of wood fuel. For this reason, wood pellets should be considered for projects where there are fuel storage limitations, or delivery limitations. Due to their small compact nature pellets can also be blown, which allows additional delivery flexibility. Through this delivery mechanism it is possible to blow the pellets down a pipe into the fuel store Wood pellets can also be purchased in 15kg bags, which are suitable for smaller domestic boilers and stoves. Wood pellets are now a very viable low carbon alternative to other fossil heating fuels and are fast becoming a major source of heat throughout much of Europe. Because of the fuel convenience, there is a large range of pellet boilers available, and many choices for the fuel feed system. It is possible to have integral fuel hoppers, free-standing fuel hoppers, outdoor tanks, or to build your own pellet store from plywood.you can then feed pellets to the boiler either via: gravity, an auger (screw mechanism) or a vacuum system. Fuel Quality Good quality fuel is essential to the efficient operation of a wood burning boiler. Boiler manufacturers will normally specify the quality of the fuel required. Specifications will include things like moisture content, particle size, and level of impurities. Using fuel that doesn t meet specifications can result in poorer efficiencies and damage to the boiler and flue system. It may also invalidate any warranties. Tel Rev 6 August 2013 P a g e 7

8 Fuelling Wood Boilers Chip Boilers Chip Boilers are operated using automatic feeding systems and are normally fed directly from a large store. These boilers are best suited for users who have a lot of space suitable for woodchip storage and access to the type of equipment necessary to move the woodchip around. Log Boilers Log boilers are always manually fed and require someone to be on site at least once per day. This is a big commitment and careful thought needs to be given to the implications. It might be okay for a hotel or a nursing home where there are staff available 24 hours a day 365 days a year. Maybe less suitable where there are no staff available at weekends or during holiday periods but heating is still required. It is not unknown for landowners with ready access to a free supply of logs to sell the logs on the market and install a pellet boiler for the convenience and automation. Pellet Boilers Most pellet boilers have an integral hopper which can be manually filled or fed automatically from a pellet store nearby. The internal hoppers can store enough pellets to run unattended for 1 week. Pellet stores can be constructed internally or externally, can store enough pellets to run for several months and are filled by a blown tanker delivery. There are many different systems for the storage and feeding of pellets some examples are as follows Example 1 shows a custom built store with a slanted floor at a 40 angle and an auger positioned along the bottom of the floor ensuring all the pellets can be used. Example 2 shows a system utilising a silo bag. This system reduces the labour involved in constructing a custom built store. This equipment enables the storage of pellets in the boiler room. Example 3 shows a feeding system utilising an underground store. This system can be useful if space inside the boiler house is limited and an outdoor storage tank doesn t fit in with the aesthetics of the building. Tel Rev 6 August 2013 P a g e 8

9 Buffer Stores Biomass boilers are generally less responsive to instant heat demands than traditional fossil fuel boilers. They don t modulate as effectively and they take longer to heat up and cool down. The work most efficiently when they have a long constant demand for heat rather than operating in a profile where they are required to be on and off constantly. In a typical building when the heating is first required the boiler fires up and stays on constant demand until the building is heated. To maintain heat requires the boiler to constantly switch on and off as the building thermostat switches. It is the maintenance of heat in the building that Biomass boilers are not very good at. Installing a buffer store is a good way of addressing this problem. A buffer store is a large tank filled with water. The water in the tank is heated by the boiler and effectively stores the heat ready for use when required. The heating and hot water systems take their energy from the buffer store. The buffer store is highly insulated so doesn t produce significant heat loss. The buffer store is always ready to give out its energy as the building requires it. This is a very effective system for heating buildings quickly as there is no need to wait until the boiler heats up. A biomass boiler and buffer store will be designed so that the boiler will only fire when the buffer store has given up enough energy that the boiler can run for a reasonable length of time between each fire up and shut down thus improving efficiency. Access to instant heat is also a real benefit. Additional heat sources such as solar panels or a back up oil boiler can be fitted to a buffer store helping to improve overall efficiencies. Maintenance Boiler maintenance requirements are slightly higher than with traditional fossil fuel boilers. The main difference is the removal of ash from the boiler. Around 1-2% of the volume of fuel burned will be produced as ash. Some smaller boilers require the ash to be cleaned out every few days. Larger boilers can have much larger ash collection systems and only require emptying every few months. Training on proper operation of a biomass boiler will be provide by the boiler installation company. It is essential that the boiler company has good relations with the customer during the first few months of the new boiler installation. Hot Water Demand Hot water is also supplied by the buffer store and can do so in a number of different ways including use of existing hot water cylinders or using special hot water modules. In the summer time when heat demand is very low it can be possible to use solar panels to meet hot water demand and keep the biomass boiler switched off. Tel Rev 6 August 2013 P a g e 9

10 Renewable Heat Incentive Phase 2: RHI for domestic installations from Spring 2014 onwards The Department of Environment & Climate Change (DECC) recently announced the introduction of the domestic renewable heat incentive (RHI). The domestic RHI scheme will pay owners of solar thermal panels, biomass boilers and heat pumps at the following levels: 7.3p/kWh for air source heat pumps; 12.2p/kWh for biomass boilers and at least 19.2p/kWh for solar thermal. The table below shows an estimate of possible benefits of replacing a 12 year old oil boiler with a new biomass boiler: This table shows the estimate of possible benefits of replacing a 12 year old LPG boiler with a new biomass boiler: These tables are meant for illustration purposes and should be used as a guide only. Check your house size, the fuel being used and current fuel costs to get a rough idea of how much better off you might be by installing a new biomass boiler. If you think your current boiler is costing too much, there has never been a better opportunity to replace it with a new highly efficient, environmentally friendly Biomass boiler. Call us and we will arrange for one of our experts to visit you to establish your home's suitability for this exciting new technology. Tel Rev 6 August 2013 P a g e 10

11 Help with Capital Costs It can be easily demonstrated that installing a Biomass heating system is very cost effective. Many customers will pay the capital costs back in as little as 3 years and their RHI payments will exceed their fuel costs. This means that not only will they be heating their buildings for free they will also have income over and above. But, the capital cost of this equipment is significant. There are other sources of assistance which we have detailed below: Energy Savings Trust - Scotland The Energy Savings Trust offer fixed rate loans of up to 10,000 to help householders to install renewable energy technologies or measures that reduce energy consumption. Funded by the Scottish Government, the scheme aims to support homeowners that are looking to replace old and inefficient technology as well as install energy efficiency measures. Contact the Energy savings trust on Renewable Heat Premium Payment. (RHPP) The Energy Savings trust will also be able to give advice on applying for funding through the RHPP scheme. This grant money is offered to anyone installing certain renewable technologies at the following rates: 2000 for Biomass boiler installs. 600 for Solar Thermal Installs and 1300 for Air Source Heat Pump Installs. It should be noted that this will money will be recovered from anyone claiming RHI. (over the 7 years RHI is payable) Tel Rev 6 August 2013 P a g e 11