Summary of our current "carbon situation"
We believe The Milll is now carbon neutral. Prior to our various renewable technology investments we used about 17,000kWh annually for lighting, water heating and electrical equipment and appliances. This is equivalent to about 9 tonnes of CO2 emissions per year. In addition we burned around 5800 litres of oil for heating. This is equivalent to around 14 tonnes of CO2 emissions. We now no longer burn any oil for heating. Much of the electricity we use is self-generated from our hydro-turbine. Depending on our usage we may be importing electricity (for example when our heat pump is on and drawing around 8kWh), or exporting it (for example during much of the summer when the heat pump is not operating). Prior to the installation of our heat pump in the course of a year we generated about 2000kWh more than we used. Since the installation of our heat pump and an all electric kitchen our electricity usage has jumped. Unfortunately 2010 was a poor year for generating electricity as a result of software problems, a failed air-valve assembly on the hydro-turbine and very low river levels in the summer. In addition by January 2011 we had suffered our coldest winter for many years. In 2010 we estimate we have used about 29000kWh and generated only 17000kWh (on a good year we would hope to generate over 20,000kWh). However all the additional electricity imported is now from a green tariff and entirely sourced from renewable sources.
Details of our various renewable initiatives
The micro-hydro-turbine
In 2005 we commissioned Derwent Hydro to undertake a feasibility study. This indicated a potential generating capacity of around 30,000kWh per year and identified a suitable location. Derwent Hydro recommended a siphonic turbine with a flow rate of 450 litres per second operating on a head of 1.4 metres and with a potential output (at 80% efficiency) of just under 5 kW. After attending to the various planning, regulatory and civil engineering issues the turbine went live at the end of November 2006. We received a grant of £5000 towards the total cost of some £30,000. At the time of its installation we received payments of around £45 for every MWh produced, plus around 7.6p per every kWh exported. Recent changes in incentive payments mean that we now receive £90 for every MWh produced but only 3p per unit for our exports. For those thinking of doing a similar thing please note that had we installed the turbine after July 15th 2009 we would be receiving around £200 for every MWh produced!
The solar panels
We decided to install solar panels because most of our hot water demand is during the summer months. We therefore thought this would reduce significantly the amount of electricity used to heat water (which we could offset against the additional electricity imported during the winter to heat the house). We ordered the solar panels from Smart Energy in 2006 but put off installing them until July 2009 because we were not clear where our hot water tank would be after our renovations. We were extremely lucky to have them installed when we did because Smart Energy went into liquidation a couple of days after the installation. Our solar panels cost around £7000. From June 2011 we expect to receive payments under the Renewable Heat Incentive for using them for heating hot water. We're not sure how this scheme will operate but the government has recently said that it will not pull the plug on these incentives despite the current financial crisis.
The heat pump
Our hydro engineers planted the idea of using our self-generated electricity to run a heat pump as it is far more economical to use our self-generated electricity than to export it. The heat pump is manufactured by Wiessmann in Germany and was installed by local company Renenergy. It has a rated output of around 27kW for which it requires between 5 and 8 kW of input (plus the occasional boost from a 6kW 3 phase immersion heater in conditions of extreme cold). The heat pump extracts heat from the river by means of heat exchange coils submerged in the river silt. The original design pumped water from the river through a self-cleaning filter and thence into a plated heat-exchanger. This design never worked effectively because it was too difficult to balance the flows between the various elements. We found that the heat exchanger would regularly freeze solid and then take many hours to defrost whereupon it would immediately freeze solid again if the heat pump restarted. Renenergy engineers spent many hours trying to ensure the pump primed effectively, replacing pumps, changing pump locations, increasing the bore of the various hoses and eventually considering changing the specification of the heat exchanger. They finally changed the design from a direct-water sourced system to the indirect system. Since when the heat pump has been operating much more effectively.
As with our solar panels we should start to receive Renewable Heat Incentive payments from June 2011 for using our heat pump to heat the house.
Our expenditure on the heat pump and associated equipment was around £23,000
The underfloor heating (UFH)
A heat pump works most efficiently when producing output water temperatures of around 45 degrees. This is not hot enough to run a radiator-based central heating system which uses water at temperatures in excess of 65 degrees. Most heat pumps therefore operate through underfloor heating schemes which have a much larger surface area and run at a much lower temperature. We have installed underfloor heating on the ground and first floor of the mill. Our top floor rooms are not heavily used in the winter and can be heated when required by small electric panel radiators. We used Eco-Conversions (sister company to Renenergy) for the design and installation of the UFH.
The heating is provided by several kilometers of high quality, flexible plastic PEX pipe embedded in screeding on the ground floor and in a dry sand and cement mix on the first floor. The pipes are connected at three manifolds which control the flow of water into each heating loop via electrically operated valves. Beneath the pipes on the ground floor there is a significant layer of rigid foam insulation to prevent downward heat loss.
The system comprises 12 independently controlled heating zones with wall mounted thermostats and controls in every zone. Each zone can be set to a different target temperature and a "set-back" temperature which it will revert to when the heating is "off". All zones can have independent switching times. One benefit of the system is that if we light our log-burning stove in the sitting room, the room thermostat will recognise this and reduce the circulation of hot water to the UFH system in the sitting room thereby saving energy. Additionally we can set our guest bedrooms to be "off" during the day but on in the morning and evening.
Our expenditure on the UFH was around £9,000
The rainwater recycling system
We discovered a disused coal cellar next to the house when undertaking our renovations. We cleaned out the rubble and tanked it. Rainwater is collected from the rear roof and sent to the tank via a filter in the down-pipe. It is delivered to the tank through a calmed inlet which prevents incoming water from stirring up any sediment. The tank contains a floating and filtered intake hose attached to a pump which pumps rainwater to a holding tank in the attic. This then delivers it to all the ensuite toilets. The system is managed by a computerised panel which detects the level of water in the collection tank (and if it is insufficient delivers mains water to the attic tank). It also measures the water in the holding tank and only refills it when it has emptied to a certain level. This stops the pump coming on every time a toilet is flushed. It also detects if the tank has not been used in the previous 24 hours, in which case it drains water in the attic tank back into the collection tank where the water remains cool and fresh. The rainwater management system (Rain Director) was provided by RainwaterHarvesting.co.uk. Total expenditure has been around £1000.
Domestic hot water
We use three energy sources to heat our hot water. The heat pump provides energy efficient pre-heating of hot water to around 40 degrees. The solar panels will provide solar thermal hot water in the summer and on sunny days in the winter up to 65 degrees. Finally we have a 3 phase immersion heater to ensure our water reaches temperatures that will remove any risk of Legionnaire's disease and to provide back up in the event of low solar radiation. The heat pump is timed to switch to domestic hot water only outside daylight hours to ensure we do not waste any available solar energy. Similarly the immersion heater is timed to boost temperatures in the evening and during the early hours of the morning.
We have a relatively large building with six bedrooms all with ensuite bathrooms. Many of these rooms are some distance from the hot water tank on the ground floor. We have therefore installed a pumped circulation to ensure hot water is available quickly at all taps at times of maximum use. The circulation system is on a timer because pumping water around the house uses electricity, loses heat and cools the water in the hot water tank.
We try to be economical with hot water because of the energy required to heat it. We therefore do not provide baths and all our showers have water saving shower heads (Mira Ecoflow). These heads mix air into the water stream and provide a very full shower experience but at a much reduced rate of water consumption.
Other elements
All our toilets have dual, low-volume flush systems to reduce water consumption and loading of our septic tank systems.
Most of our lights are compact fluorescent, low energy bulbs. We have some LED emergency exit signs, picture lights and external floodlights. When LED products become available for general lighting at a reasonable cost we will move to that technology. Our holiday cottages currently have a number of halogen downlights. I really don't like these because, despite the light quality they provide, they are hugely inefficient, create dangerous levels of heat and regularly require bulbs or transformers to be replaced. I expect to change these to 240volt GU10 LED lights sometime soon.
We have sought to reduce our exposure to volatile organic compounds (VOC) in the building by using natural, zero VOC paints for all new paintwork and water-based wax treatment for all new wood. Unfortunately we were unable to source natural, non-slip floor coverings for our wet-room bathrooms and kitchen. These are PVC-based.
We are reducing our reliance on chemical cleaning products by designing easy to clean bathrooms and E-cloths wherever possible.
Our rebuilding work enabled us to radically improve the thermal efficiency of the building by the use of rigid foam in floors and ceilings, spun mineral wool in some voids and for sound-proofing in walls, and sheeps wool insulation in the attic. Additionally practically all windows are now double-glazed. The curtain wall at the rear of the house uses 100% recyclable aluminium framing which is powder-coated and virtually maintenance free (the glass is also self-cleaning). The remaining wood, sliding sash and casement windows use laminated Scandinavian softwood.
We have an Owl wireless energy meter which enables us to measure our consumption of electricity at any time and at any place in the house. This helps to keep us focussed on minimising our importation of electricity.
Our current septic tank system pumps liquid waste to a soakaway in our field. I am considering replacing this with a micro sewage treatment plant which breaks down solids using aerobic digestion with the air supply being provided by natural through-draught rather than an air pump. This will further reduce our use of electricity and hopefully eradicate the pumps and small bore pipes which are currently prone to failure and/or blockage.
Potential impact on our guests
Our underfloor heating system is a slow-response system and bedrooms are usually set for a comfortable 18 degrees (65F). Some people may find this a bit cool if they are spending time in the bedroom. We can increase temperature on demand but it may take an hour or so to take effect. Bathrooms are set warmer, but again this is timed so use of the bathroom in the middle of the day may feel a little cool.
Our hot water is pumped but timed. Use of hot water outside the periods when we expect people to be washing (7 - 9 am, 6-7.30 pm when people are preparing to go out, and 9.30-11.30 pm when people are preparing for bed) may result in some delay before hot water arrives.
We have private sewage treatment (septic tanks) but will be installing a low energy micro-sewage treatment system at some stage in the future. Guests must not use the toilets to dispose of anything other than toilet paper. This includes but is not restricted to Kleenex tissues, female hygiene products, dental floss, condoms, plastic bags, other paper, cotton buds or cotton wool.
Economic considerations
Our investments in renewable technology were primarily motivated by a concern for the environment and a desire to use our natural resources in the most effective manner, rather than any financial payback. However with changes in the arrangements for payments for renewable electricity generation and incoming payments under the Renewable Heat Incentive our investments look increasingly attractive.
Our total capital expenditure has been approximately £70,000. This does not include insulation, new windows, bathroom items and some labour as these elements were part of the general refurbishment in any event. Against this we can identify the following financial benefits (using some assumptions)
1. annual saving of £3480 on oil (assuming 5800 litres at 60p per litre)
2. annual revenue of £1800 from Feed-in-Tariff (20,000 kWh at 9.0p per kWh)
3. annual revenue of £200 from exported electricity
4. annual savings of £1300 on electricity we have not had to import (13000 kWhs used out of 20000 generated)
Less expenditure on additional electricity imported at around £1500. Leaving a positive balance of £5280
From June 2011 payment of RHI may result in an additional incoming payment of around £1000. Suggesting a positive balance of £6280 and an annual return on investment of around 9%