40% House

David and Barbara Hammond have converted a challenging housing type in a conservation area into a showcase for renewable and low energy systems. Their renovation combines insulation, photovoltaics, solar thermal and a highly innovative heat pump heating system taking its heat from the river Thames.

The two storey terraced house was built in the mid 1860’s as part of the wholesale speculative development of Osney Island in central Oxford. The house was poorly constructed for a working class and rental market but has since become highly desirable for its central waterfront location. The house faces east, but, as an end terrace house, enjoys an unobstructed southern aspect along its side. This aspect and the close proximity to the Thames were the main inspirations for David Hammond’s highly original renovation. 

Why did they want to do it?
David Hammond is an architect with a long and passionate interest in renewable technologies and space heating using low grade heat sources such as solar collectors and heat pumps. In his architectural practice he has experienced deep frustration with the slowness of developers, planners, and clients to adopt these new technologies and wanted to show what could be done with his own house. Barbara Hammond has a PhD in Sustainable Development and works in Central Government in these areas.  David and Barbara share the deep commitment to the environment which has inspired this project.

About the renovation
The house was in poor condition and required a thorough renovation. It soon became clear that the building was also structurally unsound: the side gable wall was only four inches thick and was skewing dangerously under the weight of the roof.  This, and other structural problems, led to the decision to rebuild both roof and floors within the strengthened shell of the original house. The renovation also included a new kitchen extension at the rear of the house and a self contained office at the end rear of the garden.

The passageway along the south side of house was glazed over to create a sun porch, and sliding doors installed along most of the kitchen wall which faces onto it. The doors are closed during cold periods so that the space traps any additional  solar warming, and on sunny days and particularly during  the summer months the doors are opened up to let warmth into the house. 

Pictured: South facing solar panels with glazed lobby below

Insulation
The external walls were insulated internally with rockwool held between batons and lined with Fermacell, which David recommends over plasterboard for its strength and environmental performance. The loft was fully insulated and windows replaced with high performance double glazing in wooden frames.

Heating
It is the heating system which makes this house remarkable. The space and water heating are both fed by a large water thermal store tank (provided by Chelmer Heating), which is maintained at a temperature of 45°C by a combination of solar and a heat pump.

The five Viessmann thermal flat plates with a total area of 7.5 m2 provide the initial heat. A clever (and money saving) feature is that the large area of panels fully replaces the roof of the south facing roof above the side and rear kitchen extension. They were installed by a Viessmann recommended contractor at a cost of £3,600.

The additional ‘top up’ heat is provided by the heat pump. Heat pumps are electrically powered compressors that extract heat from the local environment and concentrate it at the temperatures needed for heating purposes. Most conventional heat pump systems have a ground source- either from a closed circuit of piping laid in trenches or in a single deep bore. A ground source was not practical on this restricted site and the Hammonds’ system draws its heat from the River Thames.

A pump lowered into the river pulls the water at a rate of 35 lites per minute through a filter and into the 1.5 inch diameter pipe which carries the water under the road and the ground floor of the house, through the heat pump, and then back into the river. The river has a higher  and more stable temperature than a ground source and the high flow levels possible with an open loop system of this kind further enhance efficiency.  The main costs for using the river was £600 for a section 50 license from Oxfordshire County Council and £1500 for the specialist contractors to dig up the road

The 6Kw heat pump cost £3,100 and is a simple and standard model from Kensa Engineering. Because of its slight operating noise it is housed in the back garden in a box the size of a small fridge. In three years the entire system has only once required maintenance- a a relatively straightforward operation to clear the water inlet of leaves.

Pictured: a 6Kw heat pump in its box in the garden

The space heating is provided through an underfloor system. On the ground floor the heating pipes are set into screed under the solid wood floorboards. On the first floor the pipes are laid between the floor joists and set into sand and cement ‘pugging’.

David describes the combination of heat pump and underfloor heating as ‘the perfect marriage’. Because an underfloor heating system requires a lower operating temperature than conventional radiators, the combination minimizes the temperature gradient- the differential between the input and output temperatures- which is the main limitation on heat pump performance.

Photovoltaic Array
There is a 1.1 Kw PV array installed by Solar Century on the roof of the office, which supplies the domestic demand and exports any surplus to the grid. It has generated 1101kwh since it was installed in October 2004. 

Pictured: David Hammond’s office with a 1.1Kw solar photovoltaic array

What were the main obstacles they encountered?
The Hammonds faced difficulties finding skilled and committed installers and have been frustrated by the difficulty in getting installers back for minor adjustments of the solar panels.“There is simply not enough competition’ they say.

However, the Hammonds reported a positive experience of dealing with the local planners. Although they live in a Article 4 conservation area, they kept within planning regulations because the solar panels were not installed on the street face of the house. The Environment Agency and council were very helpful with the paperwork and logistics of digging up the road to lay the piping for the heat pump system.

Anyone wishing to replicate the heat pump system would face a new obstacle: negotiating terms with the government’s Clear Skies programme. The programme, which was launched after the Hammond’s  project was completed, awards substantial grants for domestic solar and heat pump systems. However, due to bureaucratic oversight, it has only issued grants to closed loop systems and does not recognise ‘open loop’ heat pump systems despite their higher efficiency.

Three top tips
1. Work with your house- as this project shows, working with an existing property can inspire new and creative solutions. David says ‘there are far more possibilities and opportunities in any house than most people realize’.

2. Hire builders and workers who have the necessary skills and have sufficient support for your vision that they will acquire the additional information or skills they may need.

3. Chimneys are perfect for mounting wind turbines- providing both support and a duct for the cabling. A small wind turbine is the next planned addition to the house and David Hammond argues that one day wind turbines could be as common on chimneys as television aerials.

What were the improvements in energy performance or the carbon savings?
From October 2004 to October 2005, the heat pump has used just over 4000kwh of electicity. This is supplied at a green tariff from Good Energy at a cost of approximately £300/year for both heating & hot water. Even if this had been supplied from conventional grid electricity it would still equate to only 2 tonnes of Carbon Dioxide emissions.

CONTACTS
The house can be visited by prior appointment.

David Hammond can be contacted through his website at http://www.hammondarchitect.co.uk/

A powerpoint presentation on the house can be found at www.coinet.org.uk/ecovation