SOLAR RECOVERY HOUSES

Objetivo

A number of existing houses have been retrofitted with sunspaces and ventilation heat recovery (VHR) systems, with the ventilation air drawn via the sunspace. The principal aim of the project was to establish the potential energy benefit of using sunspaces for ventilation pre-heating, when the sunspace and VHR system are in series and how to optimise the comfort in the sunspaces.
The use of a VHR system only reduces energy consumption if it delivers necessary ventilation air to the house. This project also examines the case with which existing houses may be made sufficiently air-tight. As well as its necessity for this project, this is of general interest as the use of mechanical ventilation banishes condensation problems, endemic in the UK housing stock.
The houses selected were all quite different, so the heat recovery systems were individually configured, allowing the adaptability of the main concept to be deduced.
The retrofitted sunspaces were universally popular with the owners.
The retrofitted ventilation heat recovery systems (VHR) were also very popular, mainly because they banished condensation in the houses.
The amenity of the sunspaces was determined by the radiant and dry bulb temperatures and was enormously improved by good design of the glazing systems and modestly air tight construction. The best system was double glazed with one low emissivity coating argon filled. That unheated sunspace is used almost all year.
Payback for the energy saving measures varied from 3.3 to 25 years. Payback was dominated not by the energy saved but by the cost of the measures. The comfort in the sunspaces varied in the opposite direction: the sunspaces of most use to the clients were the most expensive, not because they were larger but because they remained at higher temperatures (without heating) in the winter and could therefore be used more frequently. Payback times would be reduced for VHR if account were taken of the reduction in condensation risk.
VHR systems were cheaper than the sunspaces and saved more energy. Using both saves little more energy.
When used for ventilation pre-heating, the temperature of the sunspace and its amenity value fall. Consumers find this undesirable.
Ventilation air can be drawn from the sunspace; but occupants often leave doors between house and sunspace open, and then the ventilation air will be stale.
Retrofit of VHR to existing houses is possible, but expensive. If doors and windows are leaky their replacement adds to the cost.
Duct leakage in retrofit situations can be a very serious problem. UK insulation standards for ducts are so far below Scandinavia, that serious heat leakage to unheated spaces can occur.
VHR systems are sized for 0.5-1.0 air changes/hour which is insufficient to source a heat pump supplying space heating in ill-insulated UK houses. Auxiliary heat will be needed.
The increased amenity in the Bath sunspace where thin frames were specially designed, points to the need for work on better frames.
The sunspaces were individually designed, and encompass a wide range of size, type and quality of air tightness and glazing. The energy contribution from different types of sunspace was consequently determined, together with the effect on the sunspace environment. The issue of sunspace design was also considered from the general perspective of achieving satisfactory levels of comfort, and avoidance of the temptation to heat the sunspace.
The system devised for the solar recovery houses uses the sunspace air for ventilation pre-heat to a mechanical ventilation system with heat recovery. Each system was individually configured to best suit each house.
A range of different sunspace designs was used, in order to assess their relative benefits. These include sunspaces constructed using high performance glazing materials and designed to be air tight, to provide the maximum source of heat for the system. In order to supply 0.5 ach -l to the house, the sunspace would undergo perhaps 5 ach-l. The effect on the sunspace environment was therefore also considered important. The issue of sunspace amenity is extended to the summer months when the problem is overheating. A mechanical ventilation system ensures the sunspace air is drawn into the dwelling and distributed to provide uniform air quality. Extraction of air from warm, humid zones balances the system so that there are no problems with pressure difference, and also serves to eliminate potential condensation problems.
The intended system includes a heat exchanger so that heat is systematically transferred from the outgoing warm air to the incoming fresh air. This has been shown (in the Superinsulated Houses, Thermie project number EE/041/82, also carried out by the University of Westminster) to operate with up to 70% efficiency. The heat gained from this exchange will actually be reduced because the preheated fresh air drawn from the sunspace, is at a higher temperature than that from outside. For most of the heating season the sunspace temperature is, however, below the temperature of the air extracted from the house. Nevertheless, a variety of different system and duct configurations were considered, to try to maximise the benefit of the sunspace heat.
In addition to the heat exchanger, further heat is extracted from the stale air by means of a heat pump. The stale air passes over the evaporator, whilst the condenser imparts heat either to the supply air or to water.

Programa(s)

ENG-ENDEMO C - Programme (EEC) of demonstration projects and industrial pilot projects (EEC) in the energy field, 1985-1989

Tema(s)

7.2 - THERMAL

Convocatoria de propuestas

Data not available

Régimen de financiación

DEM - Demonstration contracts

Coordinador

University of Westminster

Aportación de la UE

Sin datos

Dirección

35,Marylebone Road
NW1 5LS London
Reino Unido

Coste total