【正文】 rmal mass,for the normal daily cycle of heat absorption and emission,it is only about the first 100 mm of thickness which is involved in the storage greater than this provides marginal improvements in performance but can be useful in some longerterm storage options. 25 ● In the case of solid floors,insulation should be beneath the slab. ● A vapour barrier should always be on the warm side of any insulation. ● Thick carpets should be avoided over the main sunlit and heatabsorbing portion of the floor if it serves as a thermal ,with suspended timber floors a carpet is an advantage in excluding draughts from a ventilated underfloor zone. During the day and into the evening the warmed floor should slowly release its heat, and the time period over which it happens makes it a very suitable match to domestic circumstances when the main demand for heat is in the early evening. As far as the glazing is concerned,the following features are remended: ● Use of external shutters and/or internal insulating panels might be considered to reduce nighttime heat loss. ● To reduce the potential of overheating in the summer,shading may be provided by designing deep eaves or external louvres. Internal blinds are the most mon technique but have the disadvantage of absorbing radiant heat thus adding to the internal temperature. ● Heat reflecting or absorbing glass may be used to limit downside is that it also reduces heat gain at times of the year when it is beneficial. ● Light shelves can help reduce summer overheating whilst improving daylight distribution. Direct gain is also possible through the glazing located between the building interior and attached sunspace or conservatory。it also takes place through upper level windows of clerestory each of these cases some consideration is required concerning the nature and position of the absorbing surfaces. In the UK climate and latitude as a general rule of thumb room depth should not be more than two and a half times the window head height and the glazing area should be between about 25 and 35 per cent of the floor area. Indirect gain In this form of design a heat absorbing element is inserted between the incident solar radiation and the space to be heated。thus the heat is transferred in an 26 indirect often consists of a wall placed behind glazing facing towards the sun,and this thermal storage wall controls the flow of heat into the main elements ● High thermal mass element positioned between sun and internal spaces,the heat absorbed slowly conducts across the wall and is liberated to the interior some time later. ● Materials and thickness of the wall are chosen to modify the heat homes the flow can be delayed so that it arrives in the evening matched to occupancy periods. Typical thicknesses of the thermal wall are 20– 30 cm. ● Glazing on the outer side of the thermal wall is used to provide some insulation against heat loss and help retain the solar gain by making use of the greenhouse effect. ● The area of the thermal storage wall element should be about 15– 20 per cent of the floor area of the space into which it emits heat. ● In order to derive more immediate heat benefit,air can be circulated from the building through the air gap between wall and glazing and back into the this modified form this element is usually referred to as a Trombe wall. Heat reflecting blinds should be inserted between the glazing and the thermal wall to limit heat buildup in summer. In countries which receive inconsistent levels of solar radiation throughout the day because of climatic factors (such as in the UK),the option to circulate air is likely to be of greater benefit than awaiting its arrival after passage through the thermal storage wall. At times of excess heat gain the system can provide alternative benefits with the air circulation vented directly to the exterior carrying away its heat,at the same time drawing in outside air to the building from cooler external spaces. Indirect gain options are often viewed as being the least aesthetically pleasing of the passive solar options,partly because of the restrictions on position and view out from remaining windows,and partly as a result of the implied dark surface finishes of the absorbing surfaces. 27 As a result,this category of the three prime solar design technologies is not as widely used as its efficiency and effectiveness would suggest. Attached sunspace/conservatory This has bee a popular feature in both new housing and as an addition to existing can function as an extension of living space,a solar heat store,a preheater for ventilation air or simply an adjunct greenhouse for balance it is considered that conservatories are a contributor to global warming since they are often the sunspace should be capable of being isolated from the main building to reduce heat loss in winter and excessive gain in area of glazing in the sunspace should be 20– 30 per cent of the area of the room to which it is most adventurous sunspace so far encountered is in the Hockerton housing development which will feature later. Ideally the summer heat gain should be used to charge a seasonal thermal storage element to provide background warmth in winter. At the very least,air flow paths between the conservatory and the main building should be carefully controlled. Active solar thermal systems A distinction must be drawn between passive means of utilising the thermal heat of the sun, discussed earlier,and those of a more‘ active’ nature Active systems take solar gain a step further than passive convert direct solar radiation into another form of collectors preheat water using a closed circuit emergence of Legionella has highlighted the need to store hot water at a temperature above 60C which means that for most of the year in temperat