METHOD FOR HEATING AND/OR COOLING AIR SUPPLIED INTO A BUILDING

Abstract: The present invention relates to a method for heating and/or cooling air supplied into a building, the building being of the type in which air is caused to flow in through the roof (1) which is a so-called counterflow type roof, i.e. the air flowing in from outside and through the insulating layer (4) of the roof counteracts the exchange of heat through the roof, and the floor consisting of a base slab (8) preferably made of concrete. The base slab (8) is heated and cooled, respectively, by means of conduits or ducts (9) cast into or under the base slab which is used as a radiation source for heating and, respectively, as a radiation receiver for cooling the roof (1) and the air supplied therethrough.

Description: METHOD FOR HEATING AND/OR COOLING AIR SUPPLIED INTO A BUILDING The present invention relates to a method for heating and/or cooling the air in a building, the building being of the type in which supply air is caused to flow in through the roof which is a so-called counterflow-type roof, i.e. the air flowing from outside and in through the insulating layer of the roof counter¬ acts the exchange of heat through the roof, and the floor consisting of a base slab preferably made of concrete. Background of the invention It .is prior art to make buildings with so-called dynamic insulation of counterflow-type, i.e. buildings whose roof insulation, preferably in the form of a layer of mineral wool and a subjacent air-permeable pressure drop layer on which the insulation rests, is passed by air flowing from outside and inwards. The air is caused to flow in between the outer roofing and the ceiling insulation and is uniformly spread over the entire roof surface before being supplied into the building. This technique brings several ad¬ vantages. Inter alia, the air flow counteracts thermal leakage through the roof, which in many cases is con¬ siderable. Especially in premises with a high ceiling, such as industrial premises, very warm air is collected immediately below the roof where it is actually of no use but merely is a strain on the heat balance of the building. Owing to the counterflow roof, the cool outdoor air flowing in through the roof will, because of its higher weight, fall downwardly towards the floor and carry along the warm air and thus prevent the formation of a warm air cushion under the roof. As a result, the energy consumption of the building can be lowered and/or the thickness of the roof insulation can be reduced. However, there will be some incon¬ venience, particularly in summer, but also in autumn and spring, in buildings subjected to extreme thermal load, because the incoming air is too warm to provide an agreeable indoor temperature. Besides, the incoming air frequently has an increased temperature, since it has passed under the hot outer roofing. As a solution to this problem, different measures have been suggested, such as ' cooling in conventional manner by an air-con- ditioning equipment, which implies direct cooling of the air. Since this is a method which requires a great deal of energy, it often leads to attempts to reduce the supply of air, whereby the quality of the air deteriorates. What makes the method so energy-intensive is above all that the water contents of the air must be condensed. A further method that has been suggested, is cooling by means of heavy materials, such as concrete and stone, which owing to their thermal inertia can provide reasonable comfort by accumulation of cold at night and emission thereof in the day-time. However, it may be established that this method suffers from great structural and economical disadvantages, since large quantities of stone material are required to meet the building's entire demand for cooling. A third method which has been suggested is that the current of air through the counterflow roof is reversed when cooling is required, but the problem still remains since the air which enters the building somewhere, must be cooled somehow. Besides, this method suffers from the additional drawback that impurities in the indoor air will be deposited on the inside of the roof, which from the sanitary point of view is not satisfactory. In some premises having exceptionally great need of air, e.g. smoke-filled industrial premises, workshops or premises in which solvents injurious to health are used, the problem is the opposite, i.e. the air supplied in the cold season is too cold to provide adequate ventilation and at the same time an acceptable indoor climate. In other words, all the air required cannot be supplied through the counterflow roof, but a certain amount must be preheated and supplied in some other way. To reduce the building costs, it would therefore be desirable to be able to directly heat the air entering through the counterflow roof and not to need any addi¬ tional ventilation equipment in which air is taken in and preheated. Brief description of the inventive idea The object of the present invention is to maintain, in buildings with a counterflow roof and so-called dynamic insulation, cooling of the incoming air when the air temperature is high, and heating of said air when the air temperature is low, especially at high air flow rates, in a simple and cost-saving manner in respect of installa¬ tion as well as operation. A further object of the invention is to provide both cooling and heating without ' necessitating two separate systems. According to the invention, these and other objects are achieved in that the base slab is heated and cooled, respectively, by means of conduits or ducts extending in or under said base slab, and that the base slab is used as a radiation source for heating and, respectively, as a radiation receiver for cooling said roof and the air supplied therethrough. The Figure shown in the drawing is a cross-sectional view of a building according to the invention. Detailed descriptioπ ~ Of the invention The Figure shows schematically a building which uses the inventive method for controlling the temperature of the incoming ventilation air. A roof structure which is of counterflow-type and is generally designated 1, comprises the outer roofing 2, structural beams 3 and insulation 4. The beams 3 are suitably open, i.e. they have a web which allows air to pass, such that a coherent air gap 5 is defined above the insulation. The insulation may conveniently consist of mineral wool and rests on a pressure drop layer 6 which simul¬ taneously can form the ceiling. The pressure drop layer serves to uniformly distribute the air flow over the entire roof surface by the formation of a positive pressure in the gap 5, and may consist of an air-permeable cloth, a perforated board or the like. The ventilation air is blown under the roof by a fan 7 mounted on the roof, the air being uniformly distributed over the roof surface and supplied through the insulation and the pressure drop layer, as indicated by the arrows. The building rests on a base slab 8 which is disposed directly on the ground. Conduits 9 are positioned under the base slab, and a heating medium, such as water, is caused to circulate in said conduits. The conduits are preferably laid under the concrete but can also be cast into the base slab. It is, of course, perfectly feasible to heat the base slab by means of electric wires instead of conduits filled with a heating medium. In the embodiment illustrated, the heat or, respectively, the cold comes on the one one hand from a heat pump 10 which can recover energy from the ventilation air leaving the building and, on the other hand, from a deep-bored well 11, superficial ground heat or the like. To provide cooling, the inventive method is carried out as follows. Via the conduits 9, the base slab 8 is suitably cooled by accumulation at night when the price of energy is lower. To make the foundation soil assist in such accumulation, no insulation should be applied under the base slab. By cooling of the concrete slab, the roof surface can be cooled by radia¬ tion, whereby it cools the supply air and radiates less heat to the premises. Moreover, the cool base slab cools the air in the building by convection, but the major part of the heat transfer occurs by cooling of the roof surface and the supply air by means of radiation between the roof and the slab. The great 5 need for cooling in existing buildings is largely due to the fact that the surrounding surfaces are heated and act as heat radiation sources which are difficult to cool by convection by means of air which for this purpose needs to be exceedingly cool or be available in large amounts. In the physical sense, the cool base slab will act as a radiation receiver which absorbs heat radiation from the surrounding warmer surfaces, especially from the roof whose surface in its entirety faces the floor. The building described above can be heated corre¬ spondingly, by using the same equipment as described above for the cooling process. The difference is that the heating medium is heated before being allowed to pass the base slab, the heating advantageously being effected by night-time accumulation in the base slab and in the foundation soil. Floor heating is recognised as the best method for heating premises, since the air temperatures can be kept lower without the tempera- ture feeling disagreeable. Floor heating also permits low temperatures of the heating medium, which can be utilised to achieve an extremely low energy con¬ sumption by means of a heat pump. When the outdoor air passes through the insulation of the roof, it is preheated by the rising flow of heat. By radiation from the base slab, the ceiling surface 6 and the downwardly directed flow of air will also be preheated, before the air reaches the sojourn area close to the floor. As a result, also extremely large amounts of air can be supplied to the premises, even if the outdoor temperature is low, without deteriorating the indoor heat comfort. Heated and cooled concrete slabs have per se been used for a long time for heating and cooling buildings, but they have suffered from several drawbacks, Such systems have, for example, always been considered slow, since it takes much time for the slab to change its temperature as the weather changes. Moreover, the possible power output from the concrete slab is rela¬ tively limited, and consequently, in premises having a high rate of air change, the entire heating and, respectively, cooling requirement of the building cannot be covered via the floor, but supplementary systems with additional effects must be installed, which results in considerably higher building costs. By means of the counterflow roof in combination with a heated and, respectively, cooled concrete slab, one obtains, however, a surprising effect which was not earlier foreseen. Thus, the power output from the slab can be increased to a considerable extent or, vice versa, the temperature of the heating medium can be lowered with the power output retained, which increases the possibility of using low-temperature energy from solar heat and the like. This is due to the fact that in normal use of floor heating systems, the heat transfer between the concrete slab and the indoor air occurs almost exclusively by convection, since the difference in temperature between the floor surface and the surrounding roof and walls is insignificant. If the concrete slab is supplemented with a counterflow roof according to the present invention, the difference in temperature between floor and roof will be considerable, because the supply air cools or, where appropriate, heats the ceiling. As a result, the radiation share of the heat transfer between floor and roof will increase drastically. In other words, roof and floor can be said to strive to reach the same temperature. The heat balance of a building can be expressed wherein f = a ratio between the emission factors of various building materials w 0.85 2 C __> = the emissivity of black light « 5.67 W/m t = temperature of floor surface t = temperature of roof surface q. = radiation/convection from lighting, 1 machinery, staff « 25 W/m2 t = indoor temperature t = outdoor temperature "trans = transmission through walls, windows, 2 doors « 7 W/m A xxx a-ir flow m /m x hour In the formula, the first factor expresses the radiation between floor and roof, which has been negligible in previous applications. The second factor expresses the convection from floor to air and further from air to roof. The third factor expresses the heat requirement for heating in- coming outdoor air to indoor temperature. Thus, it can be calculated from the expression that in a method according to the present invention, the possible power output from the concrete slab is about 2 60 W/m at a temperature of the concrete slab amounting to 24°C and an indoor temperature of 20°C. This should be compared with conventional floor heating (the first factor in the expression above is then negligible), ό in which the possible power output is about 20 W/m at 27°C in the concrete slab and at the same indoor temperature. The entire supply of heat mentioned above comes from radiation which in previous applications has been almost negligible. In the method according to the invention, it is convenient to install large numbers of conduits in the slab, since large amounts of energy can be 'supplied to and radiated from the slab and, respectively, be absorbed and carried off by the slab. Owing to the above-mentioned advantages of the inventive method, almost 15 m3 of air per m2.and hour can be allowed to enter through the counterflow roof, without making the persons staying in.the premises feel uncomfortable and without additional heat or cold needing to be supplied but via the conduits in the concrete slab. Earlier, not more than 2-3 m 3 of air per 2 and hour could be supplied through the counterflow roof, until a feeling of discomfort arose. The invention also affords an opportunity to provide, in a simple and cost-saving manner, accumulation of energy from periods of low-price energy, for example at night, to periods in which energy is more expensive. This is possible since in most cases the requirement for air at night is small, whereby the supply of air through the counterflow roof may be reduced to a minimum. Consequently, the difference in temperature between the concrete slab and the roof surface is reduced to a corresponding degree, and thus also the radiation is reduced. These circumstances can be used for recharging by increasing the temperature of the concrete slab a few degrees at night, without energy being lost owing to an increased temperature in the premises. When the supply of air again increases in the day-time, the emission of heat from the slab will increase and, as a :result, the slab will be discharged. Finally, it should be added that wherever the specification mentions heating or heat, cooling or cold is of course possible in a corresponding manner, and vice-versa.

Claims: CLAIMS 1. A method for heating and/or cooling the air in a building, said building being of the type in which supply air is caused to flow in through the roof ( 1 ) which is a so-called counterflow type roof, i.e. the air flowing from outside and in through the insulating layer (4) of said roof counteracts the exchange of heat through the roof, and the floor consisting of a base slab (8) preferably made of concrete, c h a r ¬ a c t e r i s e d in that said base slab (8) is heated and cooled, respectively, by means of conduits or ducts (9) extending in or under said base slab, and that said base slab is used as a radiation source for heating and, respectively, as a radiation receiver for cooling said roof (1) and the air supplied therethrough. 2. The method as claimed in claim 1, c h a r ¬ a c t e r i s e d in that the base slab (8) and, where appropriate, also the foundation soil under said base slab are used for accumulation of heat or cold at times when low-price energy is available, for example at night. 3. The method as claimed in claim 1 or 2, c h a r ¬ a c t e r i s e d in that the conduits or ducts (9) extending in or under said base slab (8) are flown through by a heating medium which, as required, heats or cools the base slab.

Inventors: ERICSSON ROGER, ERICSSON, ROGER
Applicants: ERICSSON GIVENT ROGER AB
Application year: 1989
Main classification: F24D11
IPC codes: F24D5