I have been an academic electronic engineer all my working life. Having retired from university service, I was concerned to make my reduced income go as far as it can. Since a child, I was always concerned that a lifestyle relying on fossil fuels was unsustainable. Now I had the time and skills to work on minimising the use of these finite resources.
The ‘green’ systems were designed to permanently reduce the recurring costs of non-renewable energy supplies and water/sewerage. Each measure has a viable business case, though the payback can be 10-20 years. The measures also happen to permanently reduce my carbon impact on the environment.
I bought the house in 2006 with the intention that it be my home for life. I am the main occupant but have one house guest fairly regularly. Primary issues with the original house were (a) no upstairs bathroom and (b) a failing rear, lean-to utility room. I sought architects’ advice, which resulted in a 2-storey rear house extension built in 2009 adding 40% to the area of the house. It comprises a utility room and dining room downstairs and a double bedroom upstairs, used as a study/workshop. The original downstairs bathroom was converted into a shower wetroom and an upstairs bedroom became the new bathroom, inheriting the bath.
While the house was a mobilised building site, I took the opportunity to do the enabling work for ancillary water systems and solar thermal heating together with renewing the central heating and hot water systems. PV panels were installed in 2010 and the sitting room fireplace and chimney were rebuilt to install a small woodburning stove. Later, the solar thermal system and the water reuse schemes were completed.
The old house was built using traditional methods and materials. Any ventilation improvements needed to be sympathetic to the structure and air changes were reduced to the minimum necessary for each room consistent with allowing the building to ‘breath’.
Measures:
Insulation: Original house – retrofit cavity wall insulation (blown mineral fibre) and attic insulation (>370mm glass fibre) under a suspended floor. The attic hatch door has 75mm PIR insulation and edge seals. The older warm roof segments were insulated as part of the 1984 extension works (100mm glass fibre, maximum the cavity allowed). During the 2009 works the sitting room floor and downstairs bathroom floors had half the boards removed, so the flooring was replaced adding insulation hung between the joists (100mm glass fibre on breather-felt hammocks). The floorboards were reused for the new attic suspended floor facilitating its enhanced insulation. The new rear extension walls and warm roof are insulated to 2009 Building Regulations (glass fibre bats and PIR respectively). In winter, I monitored the inside walls using a surface IR thermometer and found failings in the blown fibre installation and one of the 1984 extension walls. The fibre fill was eventually remedied under guarantee. The south wall is now the only bare, clay brick wall with minimal waterproofing. Fortunately, it is sheltered from driving rain by the neighbouring house and there has not been any evidence of cavity damp-bridging. The front of the house is faced with ‘K-Rend’ coloured render (2016), which further improved its insulation performance. The faulty 1984 extension wall had a layer of 75mm PIR added and the tile cladding replaced over breather-felt.
Double glazing and doors. The house was already partly double glazed by 2006 but by 2009 all the remaining windows were replaced, matching the new extension windows and doors. The recent units feature controllable trickle vents. The front door and frame were replaced with a well-sealing set and the letterbox flap edges fitted with brushes.
A Clearview Pioneer wood-burning stove (5kW) was installed in the original, reworked sitting room fireplace in 2010. The house is in a smoke-controlled, urban area so the unit had to be DEFRA-approved. Vigilance is required throughout its use to ensure the flue temperature is maintained at 250degC. The previously shortened chimney was dismantled and rebuilt to its original height with a new stainless steel flue liner held in place with Lecca insulation pellets. To date, all the wood has been scavenged from neighbourhood tree operations. Some wood comes from the coppiced Hazels at the top of the garden’s rear bank.
Solar thermal DHW: Two Ritter CPC6 vacuum-tube panels on the rear, south-facing roof with a Resol controller heating a 210 litre HeatraeSadia Megaflow twin coil mains pressure domestic hot water (DHW) tank. Auxiliary heating is from a 30kW Worcester Bosch gas-fired, condensing ‘system’ boiler, which also drives the central heating (CH) system. I command boiler backup if (a) I know there will be demand for hot water (b) the upper store is <45degC and, if possible, when (c) the boiler is already warm. This can be remotely monitored and commanded. For biological safety the upper store is periodically taken to 60degC. On very sunny days the water in the tank can get hotter still as the panels are cooled by over-heating the tank. To prevent scalding, a thermostatic blending valve limits the DHW supply to 48degC. When designing the revised plumbing, I endeavoured to minimise the drawing lengths and volumes. Having a dishwasher reduces the need for repeated, small amounts of hot water in the kitchen.
Central Heating: The Worcester Bosch mains gas boiler also powers the CH. Further to the DHW zone, there are two independent heating zones, upstairs and downstairs. Each is controlled by a Nest programmable thermostat. All radiators have TRVs fitted except those that are zone-controlling. The warm period target temperature is 17degC all year. The zone valve logic is arranged to cool the boiler heat exchanger after a heating cycle by dumping its heat into the DHW tank.
Water systems. The two toilets have 6 litre, dual-flush cisterns fed from an attic header tank (100 litre) which is periodically filled with ground water from a shallow well in the garden supervised by a simple controller. Independent mains backup is provided by a ball-valve set at ‘low’ tank level. There is also a roof rainwater collection system with three, sheltered, black polythene 350 litre tanks sited at first floor level. The incoming rainwater is stilled in a sediment tower and then fed to the base of the levelled storage tanks. These each overflow into a soakaway beneath, resulting in crossflow that keeps the water fresh. The naturally-soft rainwater is used by the washing machine, dishwasher and the garden-watering taps. A regenerative shower pump is used to boost the pressure as some washing programs can stall if filling takes too long. The tank level is monitored using a sight tube mounted where it can be seen from the washing machine. Both the water systems use widely-available, standard parts. My plumber and I took care to make it fully compliant with BS8515:2009 Rainwater Harvesting Systems Code of Practice and the Water Regulations. Anglian Water’s website also provided useful guidance.
Energy efficient lighting and appliances. All the interior lighting use LEDs except for some HF fluorescents in the utility room. The two most significant energy consumers are the fridge/freezer (A+ rated) and sitting room TV (A+ rated) and AV rig. Next are the washing machines, both of which use electricity to heat their water. Clothes washing is done at 30degC. Preference is given to running the washing machines when there is excess PV available after the batteries are charged. Much of the AV rig is only powered when active – most of the components are ‘off’ rather than in ‘standby’. The main computer in the house is a ‘lid down’ laptop computer but with a large screen and keyboard on the desk. It spends most of its time in ‘sleep’ mode. Cooking and reheating is largely done by microwave. The hob is induction and the oven and back-up hob is gas. For hot drinks, a saucepan is used to heat just the right amount of water on the induction hob.
Photo Voltaic (PV) generation with battery storage: A single string of 10 panels giving 2.35kWp on the south-facing roof feeding a SMA ‘Sunny Boy’ inverter (2010). A Moixa 7.2kWh battery system (2022) stores any PV-generated energy which is in excess of the house demand. The stored energy is used to meet house requirements during peaks (e.g. cooking) and through the night. The PV layout mitigates the effect of chimney- and neighbouring roof (winter) shading. Because of having PV, the house was only ‘smart metered’ in 2021. The meter itself was able to show that I was actually exporting 70% of my PV. With current energy prices, this made installing a battery system more attractive. Now I only export what I can’t store or use.
Sun tunnel lighting. The new upstairs bathroom could not be lit or purge-ventilated using a Velux window because of its proximity to the neighbour’s soil stack vent. Instead a Velux sun tunnel was used in the ceiling over the wash basin. Even on cloudy days it provides plenty of daylight. It worked so well that in 2013 I fitted another over the stairwell, which transformed what was a dark, redundant space into an area suitable for displaying pictures. Both sun tunnels also have LEDs fitted to provide low-level safety lighting at night, controlled by a roof photosensor.
Ventilation. The kitchen and both bathrooms have passive stack ventilation (PSV). The waste heat from the PV inverter is ducted into the upstairs bathroom to assist driving its stack vent. To provide purge ventilation, each duct has a vertical axis fan triggered by humid activity or manually. The fans have a low cross-sectional blade area so the PSV effect still works when not on. Two are mounted on a brick wall in the attic, below the roof terminals, with a length of acoustic duct before each fan giving almost silent operation. The larger kitchen axial fan has shock-mounts so was fitted onto a roof rafter. During the building developments I ensured that the ground floor joists continued to have good under-floor ventilation.
All laundry is ambient-air dried, usually outside on the washing lines stretched between the wood store’s extended rafters. The utility room DHW tank has a 50W heat loss, despite being well insulated. This, together with a little extra cross-ventilation, can be used to finish the drying.
Benefits:
The PV and solar thermal FIT payments have until now more than covered the house energy costs. Until recently consumption was 6.5GWh/yr for gas and 1.4GWh/yr for electricity – less than half of the average for a house of this type. Since installing the battery system the expected electricity consumption will drop to 750kWh/yr. Careful thermostat deployment and more strategic use of the wood burner is getting the gas consumption to 4GWh/yr. Metered water use is less than 50 lpppd (litres per person per day). Southern Water’s figure for a single-occupancy house is over 178 litres per day.
Favourite feature
The toilet flushing system is a regularly appreciated benefit. The water in Southampton is notoriously hard and it is difficult to keep toilets clean without either repeated attention with chemicals or having a water softener. Here, I can flush the toilets as many times as needed and I just need a good toilet brush to keep them clean. The cisterns fill almost silently from the low-pressure header tank. So, guests and I can flush at night without worrying about noise. The bathrooms’ and kitchen ventilation is silent and effective.
Communal water supplies have a very low carbon impact and water reuse is not a strategic priority from a CO2 perspective. So, it is a pity that my favourite feature does not make much of a carbon saving, just a modest monetary one. However, the house energy measures are in a different league and have significant, recurring, carbon- and financial savings.
