An energy efficient 1930’s house By John Greengrass

It was decided it was time to downsize as the children had left home. I had been dreaming since I started in the building services industry to have an energy efficient home and now I had the opportunity to make that dream come true. I went back to basics and worked the scheme with the laws of thermodynamics in mind.

A 1930’s three bed semi similar to a large proportion of the British housing stock with a southerly facing rear garden was purchased. It was in poor condition and had to be refurbished. All new doors, architraves, skirtings, sills etc. were to be oak finish to reduce the need of maintenance which lowers the house’s carbon footprint. A small single storey extension was built with wet thermal solar panels on the roof ,which were at an angle to get the most from the sun in February. I did try to procure thermal solid solar panels but had to buy wet panels with all their problems regarding boiling and freezing which required a very complicated control system. I have since applied for a patent for very easily controllable solid thermal solar panels.

My idea was for the house to be like a thermos flask (cold in summer, hot in winter), the brickwork keeping the temperature in the house stable. To that end insulation as Fig 1 (to the exterior of the brickwork) and Fig 2 (to the roof) was installed with the wall insulation covered by self-coloured silicon render which was guaranteed for 25 years negating the need of maintenance therefore lowering the house’s carbon footprint.

The ground floor floor was found to be in need of considerable repair so was replaced with a concrete floor on 200mm of insulation. Underfloor heating pipework was installed in the screed.The thermal solar panels feed a primary tank adjacent, with a heavily insulated hot water cylinder (installed in the loft) gravity fed from the primary tank. On a sunny 21st of December (the shortest day in London U.K.) the temperature of the water leaving the thermal solar panels has been in access of 50°C and on the coldest days the skys tend to be clear.

The hot water cylinder is fitted with an immersion heater (rarely used), set to 40°C, fed solely from off peak electricity.  With the sun only the hot water cylinder temperature can reach 70+°C, so a thermoblending mixing valve is fitted to the outlet of the cylinder to prevent scolding and increasing the efficiency of the hot water storage.

 The primary tank is fitted with an immersion heater, set to 30°C which only operates when the ground floor slab temperature is below 18°C, fed solely from off peak electricity. It is sized to replace the heat loss of the structure when the sun does not shine.  The underfloor heating pipework is fed from the primary tank when required. The underfloor heating stops taking water from the primary tank when the primary tank’s temperature is below 25°C. The primary tank also feeds heavily insulated storage tanks when the primary tank’s temperature is above 50°C. With this system the structural temperature is kept to about 18°C, the ideal temperature for sleeping, although it does have a tendency in the summer to creep over that. In the bath/shower rooms I have fitted suitable wall fan heaters which only take minutes to heat the room from 18°C to a suitable bathing temperature. In the main reception and bed rooms, air to air heat pumps (at a cost of a thousand pounds a room installed) were installed, when the sun shines these are fed from electric solar panels. These cool or heat to the provide the temperature we require for dressing and sitting and are controlled by their internal timeswitches or remote controllers. For each one kilowatt of electricity, four kilowatt of heat is produced and as the temperature has to be raised by only a few degrees to reach the required temperature, the energy used is very small. Up to eight indoor units can be serviced by one outdoor unit. Ours have an 8 year warrantee and require no maintenance. 

Lighting is predominantly fed by the 24V DC rectifier unit so that a 1.5mm cable can normally feed 300w (60 No. 5w lamps) of equipment. The lamps are two 12V DC LEDs fed in series, which work well. Most switches are 2 way and off so that one end switches on, the centre position is off and the other end is auto. The auto position is fed from a master external Photocell Light Sensor Switch and a local Infrared PIR Motion Sensor Switch (£4.50 each).

 The property is fairly well sealed, with ventilation being provided by mains fed fans which run constantly removing a trickle of air. The system has a 20 minute booster circuit which operates when required by a humidistat (in the extract ductwork) when recording a reading over 58%RH (to prevent virus and mould growth) and push buttons by each toilet and in the kitchen to remove smells and steam. The supply fan to the house brings air in through a filter and as the property is slightly pressurized, the need for dusting is reduced. There is a heat exchanger to heat or cool the incoming air from the outgoing air as necessary. The incoming air is fed into the loft. The loft acts as a plenum. When the indoor temperature and the outdoor temperature is higher than the required indoor temperature, the extract air bypasses the heat exchanger. When the outdoor temperature is lower and the indoor temperature is higher than required indoor temperature the kitchen extract air only bypasses the heat exchanger. From the loft runs supply air ducts to each living and bedroom. The bedroom ducts take the air from the apex of the loft to heat the bedrooms. Each has a 2.4watt 24V DC fan (£4 each) which runs in the early morning for 20 minutes to prevent mould growth and is connected to operate when required by the lighting Infrared PIR Motion Sensor Switch.

 There is a south facing conservatory with an pneumatic automatic roof light set to open at 25 °C. A  fan controlled by a deferential thermostat and a maximum thermostat in the main living room (preventing overheating )feeds air to the main living room. This provides the main living room with some heat on a sunny day.

 I found these systems needed no annual inspections or maintenance except the cleaning of air filters which anybody can do.  This system has been working well for five years and saves a considerable amount of energy