Field of the invention

The present invention relates to a method for temporary reduction of power consumption for cooling of buildings .

Background

During recent years an increased use of electricity has resulted in that the production capacity and the electrical transmission network systems have been over-used. This concerns above all over-developed city centres with large shares of offices as these buildings must be provided with necessary power for lighting, computers with peripheral equipment and above all for cooling equipment. The last mentioned is of course even more of interest in hotter climates, for example near the equator.

The reason for over-use of electrical transmission network systems is the lack of accessible power for cooling machines when the offices open in the morning and all of the cooling equipment is turned on almost simultaneously. During the rest of the day the power is then further increased when the outdoor temperature increases and the supply air for ventilation of the offices needs more cooling. To be able to manage the supply during the most critical period, very radical measures may sometimes be demanded. The department of energy in a country may for example demand that the power consumption of a building is reduced by 50% during 5 hours. To increase the cost for the power which is consumed during a certain time of the day may also be a way to decrease the power consumption.

A method which has been developed to manage the lack of electrical power for the cooling machines is district cooling, where one in cities near oceans or big lakes can obtain direct cooling, provided that the water in the ocean or the lake is cold enough, by burying in the streets large insulated conduits providing the buildings with necessary cooling water power through heat exchangers, hereby decreasing the power consumed by the cooling machines. Air treatment and cooling plants that are used in this cooling method are mainly in operation only during the office hours. In which way the marine local environment will be affected in the long term is still unclear. The drawbacks with district cooling are several. The investment cost is high and the buildings must be situated close enough together and near a water system in order for it to be practically and economically possible to use district cooling. This limits the use to a great extent.

Another method which has been developed to manage the lack of electrical power for the cooling machines is evaporative cooling whereby the ventilation air is cooled by moisturising it with water. In more advanced plants both the supply and the return air is moisturised and rotating heat exchangers and driers are also used. The method may in many cases replace mechanical cooling but has its limitation in very hot climates or in hot climates with high air humidity. Air treatment and cooling plants which are used in this cooling method are mainly in operation only during office hours .

Another method which has been developed to manage the lack of electrical power for the cooling machines is the use of reservoirs for storage of chilled water coolth or ice coolth whereby the coolth is stored in water or ice reservoirs to

eliminate the power peaks during office hours, by way of a cooling machine being operating during non-office hours and cooling the reservoirs and where the stored coolth then is used to minimize the operation of the cooling machine during the hours when the electrical transmission network system is the most loaded. A problem with the cooling method mentioned above is that a separate storage plant is needed to buffer the cooling power which is produced. Another problem with the cooling method mentioned above is that it is costly and complicated.

Brief description of the invention

The problem with the need of a separate storage device to buffer cooling power is solved according to the invention by providing a method for temporary reduction of electrical power consumption for cooling of buildings according to claim 1.

As the method for temporary reduction of electrical power consumption for cooling of buildings comprises the features in claim 1, the advantage, that an uncomplicated and cost effective temporary reduction of electrical power consumption for cooling of a building can be carried out, is obtained.

Brief description of the drawings

The invention will be described in more detail below with reference to the accompanying drawings, where:

Figure 1 shows schematically a module-built house in horizontal section through a story,

Figure 2 shows schematically a slab for a module with five hollow channels (hollow cores) through which supply air can flow,

Figure 3 shows schematically a flow chart for a part of the building,

Figure 4 shows computer simulated cooling powers for the method according to the invention and the conventional method,

Figure 5 shows how an ejector increases the cooling of the room air.

Definitions

Re-circulated room air is defined as within the building re- circulated supply air and return air without addition of outdoor air.

Exhaust air is defined as the air which is leaving the building through the exhaust air fan.

Supply air is defined as the air which is conveyed into a room. The supply air may, if nothing else is mentioned, consist of either re-circulated room air, re-circulated room air with added outdoor air or outdoor air alone.

Cooling power is defined as the power which the cooling machine emits to the air.

Description of preferred embodiments

The present invention relates to a method for temporary reduction of electrical power consumption for cooling of buildings where the cooling energy is stored in slab or wall, comprising the steps of: - storing cooling energy in at least some part of the slab or the wall by means of that, during at least one period of time when the electrical transmission network system can supply the necessary electrical cooling machine power, supply cooling machine cooled supply air to channels arranged in the slab or the wall, and during at least one period of time when the electrical transmission network system is highly loaded reduce the electrical power consumption of the cooling machine and at the same time convey supply air through the building through the mentioned channels, which supply air when entering the channel is warmer than the surrounding slab surface or wall surface adjacent to supply air terminal devices, hereby using the earlier in the slab or wall stored cooling energy to cool the supply air.

in order to be able to use the invention to a maximum the ceiling surfaces may not be covered with for example compact false ceilings which obstruct the absorption in the slab of the energy generated in the room.

Conventional office buildings are provided with false ceilings which are situated at such a large distance below the supporting slab that the space obtained is enough to house the for each room necessary supply lines for example for electricity, heating, cooling, supply air, return air and data, etc. Thereby the possibility for storage through the ceiling area of the internal energy generated in the room is efficiently obstructed.

The slabs may in a known manner consist of prefabricated hollow core slabs of concrete or concrete slabs with embedded channels .

Figure 1 shows schematically a module-built house in horizontal section through a floor, more precisely the roof slab, with a number of underlying rooms A, B and the corridor C. The rooms A and B are limited by the outer walls 1, the corridor walls 2 and the room-separating walls 3. Each room A consists of three modules 4 at 3 x 1,2 m each (see Figure 2) where in each module three connected channels 5 are run through by supply air from a, in the ceiling of the corridor C situated connector terminal device 6 and supply air channel 7, which via vertical shafts connects to a fan room situated on the roof. The supply air from the module 4 is then flowing through the supply air terminal device 8 into the room A. The return air from the rooms A goes through a overflow terminal device in the corridor wall, not shown on the drawing, out to the corridor which in this case serves as collecting channel, for further transport to a fan room. The floor slab in room A is used in the same way as the roof slab for distribution of supply air. In this case to a room situated below room A. The modules 4 are laid up on the faςade walls.

Figure 2 shows schematically a slab for a module with five hollow channels (hollow cores) through which supply air can flow, of which according to Figure 1 three are connected for supply air distribution.

Figure 3 shows schematically a flow chart for a part of the building, and how those in Figure 1 and Figure 2 mentioned modules 4 are connected with the flow chart of the building.

Only one module for each room is accounted for as an example. The equipment for cooling and air-change of the building comprises a supply air fan 20 and a return air fan 21. Further, a heat exchanger 22, a cooling battery 23, and four motorised cut-off valves 24, 25, 26 and 27 are included. The cooling machine 28 supplies the cooling batteries with, for example cooling water, for cooling of the supply air. Via return air terminals 29 the return air in the corridor C is transported (see Figure 1) back to the fan room.

The plant operates in the following way: During office hours the valve 26 is closed and the rotating heat exchanger 22 is in operation. The fans 20 and 21 are turned on. The other valves are open. Outdoor air comes in through valve 24, passes the fan 20 and is cooled through the cooling battery 23 for further transportation through the slab modules 4 to the different rooms . The return air is sucked through an return air terminal device located in the corridor back to the fan room. During non-office hours the fan 20 is in operation. The fan 21 and the heat exchanger 22 are turned off. The valves 26 and 27 are open. The other valves, 24 and 25, are closed. Supply and return air now circulates in the plant from the terminal device 29 via the valve 26 to the fan 20 and is cooled through the cooling battery 23 via modules 4 again out to the rooms. This means that the room air is re-circulated in the building as no outdoor air is added.

When high electrical power capacity is available, the slabs are cooled down. As it, during non-office hours, only is room air which is re-circulated over the cooling batteries, a low cooling power is required as no outdoor air is added during this time period. However, the power may be increased by lowering the supply air temperature a couple of degrees.

Alternatively, one may use a heat exchanger between the outdoor air and the exhaust air, preferably with high efficiency, and after the heat exchange to cool down the supply air to a required temperature. The cooling machine power and the power consumption gets higher with this method.

Calculation example

Assumptions: A 10m ² office room with a facade length of 3,6 m (3 x 1,2 m module slabs) is situated at a west faςade in a hot climate. The outdoor temperature is maximum 43 ⁰ C, minimum 29°C. The supply air temperature +14 ⁰ C. Two persons are in the room between 08 - 17 hours, and internal power such as lighting, computers, printers, etc. is 25W/m ² during the same time period. The cooling power of a plant which works according to the invention is limited to 30% of that of a conventional mechanical cooling plant between 11 - 16 hours. Similar rooms are situated above and below the calculated room. The calculations have been performed with EQUA' s computer program; IDA Indoor Climate and Energy (ICE) .

If the calculation is performed so that the room temperature in the office room described above of around 10m ² does not exceed 24 ⁰ C and without any cut-down in power, a 30 1/s larger supply air flow is required in the conventional case compared to the method according to the invention. In total 70 and 40 1/s, respectively, is needed. The reason for this is that the plant in the conventional case only is in operation during office hours and that the larger part of the in the room developed power must be cooled away directly as it cannot be stored.

Figure 4 shows computer simulated cooling powers for the method according to the invention and the conventional method during the time period 00 - 24.

The electrical power for the cooling machine is normally around 50% of the supplied cooling power.

According to the conventional method maximum 1950W cooling power is required between 08 - 11 hours and maximum 2050W cooling power between 16 - 17 hours to hold the temperature requirement of 24 ⁰ C. Between 11 - 16 hours the power has been reduced to 1150W, i.e. around 55% of the maximum power which is 2050W. During non-office hours 17 - 08 hours the cooling machine is turned off.

In the conventional case the room temperature has risen at 16 hours to around 27,5°C. Here are thus significant investments required in costly additional equipment, for example cooling water reservoirs, to reach the set-up savings effects.

The method according the invention needs maximum 1100W during the time period 08 - 11 hours and maximum 1150W between 16 - 17 hours in order not to exceed the temperature requirement of 24 ⁰ C. This corresponds to around 55% of the cooling power in the conventional case. Between 11 - 16 hours the power is reduced to 600W, that is around 30% of the maximum power 2050W in the conventional case.

During non-office hours at 17 - 08 hours the cooling effect never exceeds 500W - which corresponds to a _^ supply air temperature of around 14 ⁰ C - as the room air is only re- circulated in the building and addition of outdoor air is not required, this because of that no or very few people are

situated in the building during non-office hours, i.e. during non-working hours .

From having cooled down the slab with 14 ⁰ C supply air between 16 - 11 hours (between 17 - 08 this has' taken place with re- circulated room air without additional outdoor air) the reduced power consumption during the time period 11 - 16 hours will give a supply air temperature of around 22 ⁰ C in this case. This supply air will warm up the slab from within between 11 - 16 hours at the same time as the surface layer of the slab has enough cooling capacity for the room air not to exceed the chosen temperature limit, in this case 24°C. Thus the slab is warmed up both from within and from the outside during a limited time period.

The power requirement (power x time) , in this case Kwh, corresponds with the framed areas of the power curves . As both buildings have the same insulation standard, theoretically the same amount of power is reguired during a 24 hour period, but as the invention uses the cooler night air for cooling of the cooling machines, a better efficiency is obtained which corresponds to a power saving of around 10% annually. In the conventional case the room has false ceilings .

The operative temperature (= experienced temperature = the mean value of the room temperature and the temperature on the surfaces which enclose the room) is lower than the room temperature according to the invention. As the experienced temperature is lower than the actual room temperature, it feels cooler than what the thermometer shows. In the convention case it is the other way around.

The reason for the large power and flow reduction according to the invention depends on a number of co-operating elements:

The blocking time, that is when the power consumption is reduced, is limited. The five hours between 11 - 16 hours cannot be prolonged more in this example without the room temperature rising to unacceptable levels, in the calculation example over 24 ⁰ C. This depends on the outdoor temperature, the air humidity and the degree of density in the building, the insulation level, the re-cycling level of room air, internal powers, etc. During a shorter time period it is possible to reach larger power savings than the 70% which have been accounted for in the example without the room temperature exceeding 24 ⁰ C. For example the cooling plant can be closed down completely so that the power is decreased to zero (0) during two hours .

The slab as power storage must have enough capacity (mass) and be able to transport necessary air in the hollow channels. The slab surfaces, that is the roof and floor surfaces, must be accessible, that is thick carpets, false ceilings, sound absorbing baffles, etc. must be installed in a way so that the heat transfer by convection or by radiation is not hindered to any greater extent.

The largest part of the energy developed in the room shall during the actual time 11 - 16 hours be transferred to the slab in order to during the other hours of the day be transported away with cooled supply air which during non- office hours consists of re-circulated room air.

There are a number of alternative embodiments of the now described method within the scope of the inventive idea to further reduce the cooling power.

A conceivable possibility is to reduce the supply air flow during a shorter time period when the electrical transmission network system is highly loaded. The air flow shall always be arranged so that odour from people, building materials, moisture, etc. does not become troublesome. This corresponds to a minimum air flow of around 6 - 10 1/s and person. In rooms with high internal heat development and/or very hot outdoor climate, the mentioned supply air flows are not enough, when air cooling of rooms, in order to meet the comfort requirements. As appears from the example above, according to the invention, 40 1/s and in the conventional case 70 1/s, is required to obtain a good indoor climate. If 8 1/s and person is chosen in the calculated case according to the invention, this corresponds to 16/40 = 0,4 times the original flow, that is 0,6 times lower flow during a shorter time period, corresponding to 60% lower cooling power during the same time period. The method according to the invention has, according to Figure 4, reduced the power to 30%. If during one hour the flow and/or the power together are reduced with an additional 60%, the total power use will now be 0,40 times 30% = 12% of the original 2050W. The assumption here is that a small increase of the room temperature can be accepted, in this case 0,5-1 ⁰ C.

Another conceivable possibility to reduce the cooling machine power is that, as is shown in Figure 4, to introduce in the flooring channels 41 an ejector 42, or a fan with low power, which through the driving force created by the supply air or the fan together with it sucks room air 43 which is cooled

down in the slab and after having passed the supply air terminal device 44 contributes to the cooling of the room.

In the described embodiment slabs have been used for storage of cooling energy. However, it is also possible that also, or alternatively, store cooling energy in walls such as inner and/or outer walls in buildings in a similar way.