A step towards zero-heating in residential homes
Jonathan Scott, Gokay Deveci, Martin Edge
Author:Jonathan Scott, Robert Gordon University, Aberdeen, UK
Focuses on affordable and sustainable housing for the UK. A dwelling has recently been built in the north-east of Scotland that has no dedicated heating plant, relying instead on high levels of insulation, low heat loss, solar gain and casual heat gains from lighting, appliances and body heat. The building, named the zero heating house, was designed by G.Deveci Architects in collaboration with Robert Gordon University. Aberdeen City Council is also currently involved in an ongoing monitoring project. Three phases are currently in progress to monitor the building, which embrace a life cycle cost analysis, environmental assessment and a post occupancy evaluation. The building is being evaluated over a year to confirm that very low energy running costs, together with other sustainable features, can be achieved without the need for increased capital expenditure.
The teams at G Deveci Architects and the Robert Gordon University now have considerable experience in the design of quite radical, innovative affordable housing. They have always been aware that the pursuit of affordability should not be restricted to the reduction of capital cost. Affordability also involves aspects of sustainability. We should be aware of the life cycle, energy and environmental implications of affordability.
The truly affordable house; that is the kind of house which is affordable both to society and the individual occupier; must represent a practical, sustainable kind of development. The zero-heating house is the latest development in our thinking about affordability in housing and the demonstration project in the private sector seeks to validate the design as a model for future development.
The design for this demonstration project is a development of Scottish homes and others previous commitment to research into affordable housing through the affordable rural housing project. Whilst the immediate output from that project has been the current 2000 homes award winning development at Kincardine ONeil, the primary characteristics of which are cheapness, flexibility and extendibility, a number of other designs produced by the ARH project have been developed by G. Deveci Architects. These designs, though also emanating from the idea of affordability, have had a number of different types of objectives.
One of the designs developed from the generic concepts explored in the ARH project has now been built by G. Deveci Architects. This is the Van Midden House, a family dwelling using lightweight composite timber I beams and sheet materials, which has been built for a private client with the aid of a Scottish homes rural home ownership grant. The design employs the concept of buffer zones, whilst its structure allows for large amounts for insulation, giving it exceptionally low U values and low energy consumption. The house also has a series of other environmental advantages related to the materials used, the disposal of waste and the way in which the development addresses the use of the site.
The local sourcing of timber materials, to replace some of the large amounts of imported timber currently used in housing, is an important aim of the design. The Van Midden house achieves these savings at a capital cost some 30% lower than standard specification, off-the-shelf kit houses of equivalent size. Initial, ad-hoc monitoring has demonstrated a high degree of satisfaction from clients and the house has recently received a National RICS award.
The zero heating house was designed to deliver radical environmental improvements over current standard housing. A particular aim was to reduce the need for dedicated heating plant to be as close as possible to zero. The precedents for housing with these kinds of aims have tended to be one-off, high cost designs, which have made environmental improvements at the expense of economic affordability. They are typically not replicable designs, which can be applied to a mass market for affordable housing. The zero heating house, despite being a single, prototype house, aimed to deliver these improvements at an initial capital cost no greater than that of standard, low cost, spec-built mass housing. In order to achieve this, the design incorporated a number of technological innovations in its construction.
The principal aim of this design was to ensure that, as far as possible, all the heating needs of the house can be derived from internal gains such as lighting, cooking, human body heat etc.
The energy efficient specification includes;
Many aspects of the design are not conceptually new, but the innovation lies in the conjunction of different innovations and the fact that they have not hitherto been used in the construction of housing in the UK The main thrust of the idea for this building was the elimination of dedicated heating plant was through the use of insulation between 300 and 400 mm thick. The zero heating family home is built using timber "I" beams that are simultaneously quick to install, and are less expensive than traditional construction. Glue has also eliminated from the construction. The crucial advantage of these "I" beams, however, lies in their increased depth, which allows extremely deep insulation to be incorporated into the structure without any cost penalty in terms of additional structure.
Ventilation, however, is just as important as heating, in order for the building to function properly. The design therefore incorporates heat recovery in the mechanical ventilation system.
Externally, the building is clad in locally purchased larch cladding with clay pantiles, both of which have expected life spans of around 60 years. Consideration of life cycle cost also included ultimate demolition and disposal and the cladding materials have some re-sale value.
The glazing is mostly south facing, with most of the north, east and west glazing eliminated. This allows daylight to enter on the south facade while reducing the risk of heat loss on the remaining facades. The glazing is also triple glazed, krypton fill with low E glass and the rooflights are double glazed low E.
The interior floor is exposed concrete, acting as a thermal mass, with 300mm of insulation beneath.
The interior of the building is more open than conventional, cellular homes, which allows heat to circulate more effectively. Another innovation is the near elimination of dedicated circulation space by allowing all rooms to run of the central living space and balcony. As a consequence most of the interior space is two storey, which allows light to flood in for long periods of the day.
In addition to the added insulation, passive solar design, thermal mass, mechanical heat recovery fans and triple glazing, a solar panel was installed to aid the water heating of the house. A wood stove is also included in the central living space as a back up during winter, though preliminary calculations suggest that internal temperatures inside the house over the year should not fall below 14oC.
Maintenance and Life Cycle
A key factor in producing innovative affordable housing is ensuring that capital savings are not secured at the expense of life cycle characteristics. There are obvious life cycle advantages to the zero heating house, but these need to be set against the maintenance profile. A research exercise looking at life cycle cost has been completed in conjunction with a life cycle cost group at the School of Construction, Property and Surveying of RGU, which has been developing software to facilitate building life cycle cost models, in a project with Salford University. Any innovation involves an element of risk taking and it is incumbent upon us to learn about and minimise the risks.
This project carried out a life cycle cost analysis of the zero-heating house and then compared this project both with a house of the same spatial design but conventional construction, and with a standard spec-build house of a similar floor area (approximately 130m2). The life cycle cost analysis was the first stage of a monitoring and assessment exercise for this project. The costs-in-use (life cycle costs) include capital, maintenance, replacement, operation and residual with particular attention given to the comparison of energy costs.
The life-cycle cost study demonstrates, to a high degree of confidence, that for all realistic scenarios over a 60 year life-span, after discounting future costs, the zero heating house makes savings of between £10,000 and £40,000 over different alternatives.
These savings are manifested for initial capital cost, energy running cost, operation and disposal cost and residual value. Only in the area of material maintenance is there a marginal (2%) cost increase for the zero heating house.
In its primary aim of reducing heating costs the zero heating house succeeds, on paper, in reducing annual heating costs to £43.40 for a gas fired heating system. This represents an 84% saving over current standard housing designed in accordance with modern building regulations, before discounting. The zero heating family home achieves a SAP rating of 123.
Total energy costs for the zero heating family home, including all the energy efficient features, succeeds, on paper, in reducing combined annual energy and maintenance bills by £300 per year (at 2.5% discount rate). This represents a 21% saving over current standard housing designed in accordance with modern building regulations.
The additional fabric insulation, triple glazing, heat recovery ventilation units and solar powered water heating allow for a 84% reduction in the heating CO2 emissions between the alternatives. The use of a wood fire also complements this environmentally as the fuel is, at least potentially, from a sustainable source.
With all the energy saving features combined, savings of up to 21% at a discount rate of 2.5% may be obtainable on the operational costs only, and have a quicker overall payback period of 19-21 years. If the solar panel is not included in the design the payback is between 8-10 years, the solar panel having a payback of around 40-45 years. It should be added that the additional cost of the zero-heat house, noted below, is the cost over and above that of the Van Midden House, with the same spatial design and broad construction technology, but without the more innovative energy saving measures (table 1).
The zero heating house is an affordable, replicable model for housing which can deliver very large environmental improvements at costs consistent with, or lower than, the cheapest housing currently on offer by our builders of mass housing.
Further savings may be available by moving from a one-off, prototypical construction by a small builder, to a more standardised, volume production.
The Team of G. Deveci Architects and the Robert Gordon University is currently investigating future variants of the design, which will refine it and develop its potential advantages. In particular there is great potential to improve local and regional supply chains for the materials used in the house and in reducing embodied energy.
Research and Monitoring
The construction of the house was completed at the end of December, 1999. The Robert Gordon University has been funded by Aberdeen City Council to complete a three phases monitoring and assessment exercise.
The three phases are;
;Results from the three phases will be used for adapting future projects for the greater use of simple energy efficient design.
Gokay Deveci, Tel ( : 01224 263714; Fax: 01224 263777; E-mail: email@example.com
Robert Gordon University
Jonathan Scott, Tel ( : 01224 263710
Aberdeen City Council