GB2505411A

GB2505411A - Air conditioning system comprising a cold object for cooling air

Info

Publication number: GB2505411A
Application number: GB1215210.4A
Authority: GB
Inventors: Matthew James Walker
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-08-27
Filing date: 2012-08-27
Publication date: 2014-03-05
Also published as: GB201215210D0

Abstract

As part of an air conditioning system, a material is used to reduce the temperature of air, where a cold object is cooled or frozen and air is then passed over it in order to reduce the temperature of a room. Preferably, the material has a high thermal conductivity running through it, to absorb energy from the air as quickly as possible, and thus increase the speed at which the air passing over or through the cold object is cooled. In use, the cold object could be placed in a home freezer and, once cooled, removed from the freezer and placed in front of a fan. The cold object may be shaped to slot into a freezer drawer and then be transferred from the freezer for attachment to the front of the fan. Preferably, the material comprises water or ice.

Description

CoolFan This invention relates to an energy efficient way of cooling a room.

Background

Many residences, in particular energy efficient flats that have been built in recent times, can get particularly hot in summer. Methods used to make the living space more comfortable include 1. Using a simple fan This is a very simple and effective way of feeling cool, but doesn't actually reduce the temperature of the room 2. Using a water-cooled fan This method of cooling passes air over water, which is cooled through energy being taken from the air by evaporative cooling. This does cool the air, but is not a fast way of cooling the air and has the effect of increasing the amount water vapour within the air, increasing humidity.

3. Using a traditional air conditioning system The traditional air conditioner is a heat engine that cools the air by rapidly expanding an inert gas, which absorbs the heat in the air passing next to it. The gas is then compressed, with the heat created by compression expelled through a pipe.

The benefit of this system is that the cooling is instant. The downsides are that:- * The compressor can create a lot of noise in many cases * The process is very inefficient, taking a lot of energy and cost to run the air conditioner.

* The pipe used to expel the hot air side product has to be hung out of a window, which can be unsightly and depending on the location of the flat may be quite loud.

Statement of Invention

To overcome the issues described above, the present invention proposes a more energy efficient method of designing an air conditioning system.

Carnot's theorem states that the maximum efficiency of a heat engine is governed by the following formula:-tlmax = 1 -TC/TH = (TH -Tj/TH where T, is the temperature of the cold reservoir TH is the temperature of the hot reservoir Using the above formula, it can be seen that as TH -0 L the more efficient the heat engine becomes. Therefore cooling an object slowly before it is used to reduce the temperature of air passing over it will be more efficient than cooling an object instantly (such as the expanding gas in a traditional air conditioner).

An example of how to achieve this could be that an object could be placed in a traditional home freezer. As the object cools, its temperature will reduce and therefore become closer to the temperature of the freezer. As the object's temperature approaches the temperature of the freezer, the energy required to cool it further decreases. The object, once cooled, would then be removed from the freezer and placed in front of a fan which would disburse adjacent cooled air around the room.

Preferably, the object to be cooled would be of a shape that easily slotted into an average freezer drawer and could easily be transferred between freezer and fan. Additionally the invention should be designed so that the transferred object would easily attach to the front of the fan.

Preferably, you would have thermally conductive materials to absorb energy from the air as quickly as possible, as the fan blows the air over the cooled material.

Preferably, you would choose a material to cool that requires a large amount of energy to absorb from the air before reaching ambient temperature. This could be done by choosing a material with a high specific heat capacity, and also a high latent heat of fusion, with the melting point of the object being between -15°C and 25°C so that melting is required.

Another way of achieving this gradual cooling would be to have a refrigeration unit built into the fan unit. This could then refrigerate overnight, and avoid the need to transfer objects between a freezer and the fan.

Again, preferably you would use a material for cooling with the same properties as above, and also have a conductive material to cool the air as fast as possible.

Worked example

Say the dimensions of a typical bedroom in an energy efficient flat is 4m * 4m * 2.5m, giving a total volume of air of 40m3. We will use generic workings for in3 and then apply to these dimensions.

Energy required to reduce temperature of 1m3 air The energy required to be removed from air = [mass * specific heat * temperature fall] Assumptions @20°C Density of air = 1.205 Kg/rn3 and therefore mass = 1.205kg @40°C Density of air = 1.127 Kg/rn3 and therefore mass = 1.127kg Specific heat of air between temperatures of -50°C and 40°C (all relevant temperatures) = 1.005 kJ/kg/°C There room is a closed system i.e. no energy escapes or enters the room.

Workings Energy required to be removed @20°C = 1205kg * 1.005 kJ/kg/°C = 1.211 kJ/°C @40°C = 1.127 kg * 1.005 kJ/kg/°C = 1.133 kJ/°C We will use 20°C figure for prudence in our calculations, and therefore the energy to be removed from the air will be 1.211 kJ/°C/m3.

Cooling material There are five characteristic priorities I have identified for the cooling material to be used 1. Non-toxic (bits won't flake into the air etc.) 2. Melting point between -15°C and 25°C 3. High Latent heat of fusion 4. High specific heat 5. High conductivity (or good method of heat transfer between air and material) Basically, we need a material that requires the maximum energy to change temperature from the temperature within a freezer (-18°C), to comfortable room temperature (i.e. 20°C) Water appears to be a good candidate for a material to use (there may be better materials identified in the future), and therefore we will use water in our worked example.

Energy to transfer from air to material = [mass * specific heat of cooling material * temperature fall] + [mass * latent heat of melting (if the cooling material changes state as part of the cooling process)] Assumptions Specific heat capacity of water = 4.186 kJ/Kg/°C Specific heat capacity of ice (@-20°C, but assume constant) = 1.97 kJ/Kg/°C Latent heat of melting/fusion = 334 kJ/Kg/°C Assume freezer temperature of -18°C Assume reduction in room air temperature required is 10°C (from 30°C to 20°C) Workings 1. The temperature of the material must rise 18°C as Ice 2. Must melt 3. Must rise 20°C as water Therefore, energy required = 1. 1.97 * 18°C = 35.46 kJ/Kg 2. = 334 kJ/Kg 3. 4.186 * 20°C = 83.72 kJ/Kg Total = 453.2 kJ/Kg

Summary

Using the bedroom example of a 40m3 room, energy required to reduce the temperature from 30°C to 20°C:- 40m3 * 10°C * 1.211 kJ/°C/m3 = 484 ki Applying the above cooling material calculation implies we would need:- 484 ki / 445 kJ/Kg = 1.068 Kg water/ice Bringing back in the size dependency, we would require 26.7 g water/ice per m3 of room that required cooling.

Claims

Claims 1. The material used to reduce the temperature of air, as part of an air conditioning system where air is passed over a cold object, should be cooled/frozen prior to air being passed over it to reduce the temperature of the room.
2. The material, as referred to in claim 1, should have another material, which may be the same as the cooled material, with a high thermal conductivity running through it, to increase the speed at which the air passing over/through the object is cooled.