The field of technology is preventing water vapour in the air from condensing onto surfaces. Refrigeration and freezer equipment in shops, and cold storages and frozen food storages require heating for the cold outer surfaces such as window panes and frames. Heating prevents condensation water or ice from generating on the cold surfaces. For heating, electrical resistors are used. With the aid of this invention, the power of the electrical heating resistors may be controlled more precisely than with the methods in use until now.

Prior art

Patents have been granted for the power control of heating resistors, such as US 5899078 A (Mager Malcolm 4.5.1999), WO 9842163 A (Libey Owens Ford Co 24.9.1998) and WO 2005030013 (Nyhlen Jonas 7.4.2005). The above inventions have not, however, been brought into use in refrigeration equipment or storages.

Compared to the aforementioned inventions, this invention is reliable and simple. At the moment, there are three prevailing practices on the market as regards the use of heating resistors. The first one is that heating power is constantly on at 100% power. This practice will be abandoned along with modernization of the equipment stock and increased awareness of saving energy consumption.

The second prevailing practice is that the heating resistors are controlled by temporally pulsing the power supply, for example, five minutes on, five minutes off. The pulsing of power must be set manually, which is why it is seldom used.

A problem exists, among other things, in the form of seasonal changes in the humidity of the environment, which results in that the control values should be changed according to the seasons to match with the changed conditions. Otherwise, the outcome is that the heating power is too low, in which case condensation is generated, or the power is too high, whereby more energy is consumed than would be necessary. The third common method is to connect a humidity sensor to the automation. The humidity sensor measures the air humidity in a shop. Controlled by a signal from the humidity sensor, the on time of the heating resistors may be extended when the humidity level in the environment is high. In winter, for example, when air is drier, the heating resistors are on for a shorter time and energy is saved.

The problem with this arrangement is its imprecision. Air humidity does not directly determine how much a condensing surface needs to be heated so that no condensation would be generated on it. In the end, it is up to the user to decide what the heating power will be with different air humidity contents. This, in turn, leads to the user adding a "safety factor" in order to avoid condensation problems, whereby energy consumption increases. This practice is described in the publication RS8GM222 Type AK-CC750 080Z0130, page 76 "Anti sweat heat control", by Danfoss.

Benefits of the invention

Condensation is generated when the temperature of a surface decreases to the dew point temperature or below it. The advantage of the invention is that the control of the heating resistors is more precise, and its final importance is in the energy savings achieved. Energy saving may be most noteworthy depending on what the initial level of the technology in use is. The equipment is independent of other technology and automation in use, and may well be brought into use for existing refrigeration equipment.

The measurement and control system according to the invention is in practice a simple and reliable method for preventing condensation from generating onto a surface.

By means of this invention, there is no need to estimate the relationship between air humidity and heating power on the generation of condensation. The result is energy savings without the risk of condensation.

This measurement arrangement according to a patent claim differs substantially from the patents US 5899078 and WO 2005030013 and WO 9842163, for example.

The publication WO 9842163 presents how condensation generation is prevented on a glass surface by means of an optical sensor.

A characterising feature of this invention is that the generation of condensation is prevented on both glass surfaces and on other surfaces as well, and this invention does not use an optical sensor. A feature of this invention, differentiating it from the patent US 5899078, is that it is based on the use of a condensation sensor, in other words, in accordance with the patent US 5899078 it measures the change in the electrical conductivity of a surface as condensation is generated. In the measurement arrangement according to this patent claim, electrical conductivity is not measured.

This invention also differs from the patent WO2005030013. A definitive difference is that according to a patent claim of this invention, temperature is measured on a surface where condensation is not wanted, such as a window pane or frame. The cold surfaces are usually the surfaces of the refrigeration equipment on the shop's side, on which it is desired that generation of condensation be prevented. If, however, situations emerge where harmful condensation is generated on inner surfaces of equipment/window panes, this, too, may be prevented by the arrangement according to this invention.

The system includes air humidity and temperature measurement sensors, and additionally a cold surface temperature sensor. The control arrangement included in the invention takes place at a central processing unit. The central processing unit provides an output signal which is used, in a manner known per se, to control the power of the heating resistors.

The aim is to position the cold surface sensor on the coldest surface of the refrigeration equipment, where harmful condensation will first be generated. The problem may be that the coldest spot is not always known and the location of the coldest spot may vary.

In practice, it also needs to be taken into account that the humidity and temperature conditions are different in different areas of the shop. If need be, the situation may be remedied by deviating measurements and this way compensate for the imprecision caused by the location of the sensors. The required deviations may be performed through the central processing unit.

An advantage of a patent claim according to this invention that a cold surface may be measured with a plurality of surface sensors at different places of the refrigeration equipment. A piece of refrigeration equipment may have surfaces that clearly require different heating power levels, whereby the need exists to measure the surface temperatures of them separately and to control their heating power with dedicated control circuits. By the measurement and control method according to the invention, a plurality of pieces of refrigeration equipment may be controlled with one central processing unit, for which at least one sensor measuring the humidity and one sensor measuring the temperature of the air are needed, as well as one or more surface sensor and the required number of separate control circuits. Each control circuit has its own output for controlling the power of the dedicated electrical heating resistors. An advantage of a patent claim according to this invention is that, out of a plurality of measurements by a surface sensor, the measurement providing the coldest reading may be selected as the value affecting the control.

A further advantage according to this invention is that it is easy to affect the final set value of the control. With the arrangement according to the invention, the temperature of the condensing surface is controlled so that the surface temperature is slightly higher than the prevailing dew point temperature. The central processing unit offers the chance to set by how much, such as 0-3° C, the final set value exceeds the dew point temperature. This temperature increase will from hereafter be referred to as "safety temperature difference". The value of the safety temperature difference may exceptionally be zero or even negative. It is obvious that the more condensation will be generated on a surface the more the surface temperature is below the dew point temperature. The practical situation, however, decides how much condensation there may be before it is considered harmful.

Basic idea of the invention

With the inventive measurement arrangement, the relative humidity and temperature of the ambient air is measured. From the humidity and temperature values obtained by measuring the air, the dew point temperature may be calculated in a manner known per se. The arrangement additionally includes measuring the temperature of a condensing surface, such as a window pane or frame. The temperature of the condensing surface is continuously controlled by the method according to the invention so that the temperature stays slightly above the dew point temperature.

In the following, the invention will be described with reference to the attached schematic Figure 1 . 1 . measuring relative air humidity Rh % and temperature Tair

2. measuring temperature I surface of condensing surface 3. calculating dew point temperature Td

4. safety temperature difference Td +ΔΤ to be added to dew point temperature

5. set value∑Td of the condensing surface is the calculated dew point temperature added by the safety temperature difference∑Td =

Td + ΔΤ.

6. when the set value∑Td of the condensing surface is higher than the measured surface temperature I surface, a signal from the central processing unit gives the command to lower the heating power. 7. when the set value∑Td of the condensing surface is lower than the measured surface temperature I surface, a signal from the central processing unit gives the command to increase the heating power.

The temperature of the condensing surface is controlled by a method according to the invention, described below.

1 The relative air humidity Rh % and temperature Tair are measured. In addition, the temperature Tsurface of the condensing 2 surface is measured. At the central processing unit, the dew point temperature Td is calculated in a manner 3 known per se based on the relative humidity and temperature measured from the air. The safety temperature difference ΔΤ is added to the calculated dew point temperature 3. The calculated dew point temperature 3 added by the safety temperature difference 4 ΔΤ is the set value 5∑Td of the surface. If 5∑Td the set value is higher 6 than the measured temperature of the surface 2, the heating power is decreased by means of a signal from the central processing unit.

If 5∑Td the set value is lower 7 than the measured temperature of the surface 2, the heating power is increased by means of a signal from the central processing unit.

An embodiment comprises a measurement and control method for controlling the temperature of a condensing surface, in which method the prevailing dew point temperature 3 is calculated by measuring the air humidity and temperature 1 . A safety temperature difference 4 is added to the calculated 3 dew point temperature, and their sum 5 is used as the set value for controlling 6,7 the temperature of the condensing surface. In an embodiment, in the above measurement and control method for controlling the temperature of a condensing surface, a temperature difference 4 having a negative value is added to the calculated 3 dew point temperature, and their sum 5 is used as the set value for controlling 6,7 the temperature of the condensing surface.

In the above, measurement and control methods according to the claims have been described. A person skilled in the art will understand the general technology and control methods of PID control, for example, by means of which an end result of the type described may be achieved. In this context, it is unnecessary to describe in detail the control technology because the same result may be achieved by using different control technologies.

All the measurement sensors are connected to the central processing unit, where the measurement results are processed and the control values calculated. A heating control signal is obtained as the output of the central processing unit. It is obvious for a person skilled in the art how heating power may be controlled in a manner known per se by the control signal from the central processing unit.