WO1981002638A1

WO1981002638A1 - Method and apparatus for determining heat loss

Info

Publication number: WO1981002638A1
Application number: PCT/SE1981/000062
Authority: WO
Inventors: B Nilsson
Original assignee: Thermius Elektronik; B Nilsson
Priority date: 1980-03-04
Filing date: 1981-03-04
Publication date: 1981-09-17
Also published as: JPS57500446A; EP0054027A1; AU6787981A

Abstract

Method and apparatus for determining the heat loss of for instance a human or a heated building depending upon the current climate. The principle is based upon an analogue method of simulation and includes a heated climate sensing body. The heat flow is being simulated by a corresponding electric current (1). The skin's respectively the wall's thermal resistance is being simulated by a corresponding electric resistance (R). The body temperature and the surface temperature of the skin or the inner- and outer temperature of the wall are simulated by two corresponding potentials (Ub resp Us) appearing on each side of the electric resistance (R). The current (1) is being measured by means of for instance one in the heat flow or in effective temperature calibrated instrument.

Description

METHOD AND APPARATUS FOR DETERMINING HEAT LOSS

The present invention relates to a method and apparatus for climate measurements such as for detexinining the human heat loss of as well indoor as outdoor climate for the control of climate in buildings.

It is since long known that the degree of air movement in particular but also humidity and heat radiation from the sun determines the degree of cooling acting upon both humans and buildings. Empirical studies made for instance during admiral Byrd's expedition to the Antarctic in 1939-1941 show that the human experience of for instance an air temperature 0ºC and an air movement 20 m/sec. is equal to a teπperature of -20ºC and windstill.

Described in the Patent Specifications Nos. SE 7114749-0, DE 1.798.439, DE 2.210.523 and DE 2.528.340 but also in the Swedish Publication 'Ny Teknik , 1973-12, page 5 and in 'Heating/Piping/Air Conditioning , January 1973, page 139144 as a known method to utilize one electrically heated body as a sensor in an apparatus measuring the degree of thermal discomfort especially in indoor climate and where the conveyed electrical power is a measure of the heat loss of the body.

It is also a known method to supply the climate sensing body with a thermal resistive material in order to simulate the thermal resistance of the human skin. Described in SE Patent Specification No. 7114749-0 is another method for simulating this thermal resistance where the loop gain of the temperature regulation system is being reduced so that a regulation error is obtained.

The heat flow which leaves the human body through the skin is to be formulated as

Q = (T_b - T_s)/z 1) Q is the heat flow per unit, area of the human body Ts is the surface temperature of the skin z is the thermal resistance per unit area of the skin T_b is the internal teπperature of the human body, normally 37ºC.

In an apparatus according to the invention the heat flow is being simulated with an electric current (I), the thermal resistance of the skin withan electric resistance (R), the skin's surface with an electric potential (U_s) and the temperature of the human body with an electric potential (U_b). The electric current which flows through the electric resistance may be formulated as

I = (U_b - U_s)/R 2)

The electric resistance (R) together with the two electric potentials (U_b ) and (U_s) are thus affecting the electric current according to the expression 2) in the same way as the thermal resistance (z) together with the two temperatures (T_b ) and (T_s) are affecting the heat flew according to the expression 1). If we suppose that the relation between an electric potential and temperature can be expressed as U = k . T 3)

where k is a constant we get according to 1) and 2) that the relation between the electric resistance and the thermal resistance may be formulated as R = k . z 4)

For a heated building a similar argumentation may be applied. If in this case T_s indicates the temperature of the wall's surface and T_b the temperature of the walls inner surface and z the thermal resistance of the wall then the heat flow Q through the wall will be described according to 1). In figure 1 an example of an apparatus is being illustratedbased upon the invention. The apparatus is supplied with a constant voltage of for example 5 Volts. The transistor (T1) and the linear temperature sensor (D1) are thermally connected to each other and also to a climate sensing body which is affected by the climate one wants to measure. The climate sensing body may in practice be made of a cylinder of metal with the dimensions Φ 10x30 um with a durable surface. The current (I) which flows through the transistor (T1) for instance of type BD 529, will cause that the transistor (T1) but also the temperature sensor (D1 ) which in practice can be the silicon diode 1N 914 and the climate sensing body are being heated up to the temperature (T_s). the resistor (R1 ) together with the temperature sensor (D1) will make that one to the temperature

(T_s) proportional potential (U_s) is obtained. With the two resistors (R₂) and (R₃) a potential (U_b ) is obtained which is proportional to (T_b). The resistor (R) which is flown through by the current (I) simulates the skin's thermal resistance.

The current flowing through (R1) and (D1) is as well as the current through (R₂) and (R₃ much less than the current (I) and could be entirely neglected. The operational amplifier (OP1) could for instance be of type 2740. (OP1) has a high amplification for example 100000 times and controls the current (I) through the transistor (T1). With the high amplificatiαn of the operational amplifier (OP1) the voltage difference between the two inputs may be considered to be nil. This allows then the following relation to be formulated

U_b = U_s + R . I 5)

which after reformulation results in 1 = (U_b - U_s)/R

i.e. an expression identical to 2) above. The heat flow according to expression 1) can thus simply be measured with an apparatus according to the invention by utilizing one, for instance in a heat flew, Clo-units, or in the equivalent temperature of a stationary air volume calibrated instrument which measures the current (I) and where the thermal resistance is determined by the electrical resistance (R).

The apparatus described has considerable advantages to those described in the Patent Specification mentioned in the introductory paragraphs. According to the present invention the skin's thermal resistance is being simulated with an electrical resistance. This method is considerably siπplier to apply and results in a greater precisian in the simulation than the method of furnishing the climate sensing body with a heat insulating layer. It is difficult to furnish a climate sensing body with a defined layer which has a durable surface which has stable thermal qualities and which has a defined and constant thermal connection to the climate sensing body.

In the Patent Specification SE 7114 749-0 the thermal resistance is being simulated with partly a heat insulating layer but also partly owing to the fact that the locp gain of the taiperature regulation system is being reduced so that a certain regulation error will occur. The way of the present invention is even in this case considerably siπplier to apply and will result in a greater precision in the simulation of the thermal resistance.

According to well kntwn theories of feedback control systems, a low loop gain will result in substantial regulation errors. In general this is not wanted as irrelevant parameter variations in the systan will influence the regulated or simulated quantity in a negative way, but also that the regulated or simulated quantity in itself not beccmes entirely defined.

In an apparatus according to the invention the influence of-the human perspiration on the heat loss to the envirtnment is simulated allowing water to evaporate from the surface of the climate seising body with a porous surface which is being moistened with water. Depending on the humidity of the surrounding air mass a more or less rapid evaporation of the water will occur. This effect will cause a more or less great heat loss from the climate sensing body. In an apparatus according to the invention the effect of air movement is regulated by means of a suitably formed shield which to the extent desired limits the cooling of the climate sensing body. The shield can for instance be made of a finemeshed net or a in a suitable way perforated can which encloses the climate sensing body.

Claims

1. Method for determining heat loss especially with humans but also with buildings characteri zed in that the heat flew decipated via the human skin or the wall of the building is simulated by the corresponding electric current (I), that the thermal resistance of the skin or the wall is simulated by a corresponding electric resistance (R) flown through by a current (I) that the human body temperature and the skin surface teπperature or the inner and outer surface temperatures of the wall are simulated by two corresponding electric potentials (U_b ) and (U_s), and that the voltage drop across the electric resistance (R) is regulated to become a certain function of the two potentials U_b and U_s.

2. Method for practising claim 1 characteri zed in that the electric current (I) is measured by a device calibrated in teπperature equivalent to the temperature of a still moisture saturated air mass which causes the same degree of heat loss as the actual climate.

3. Apparatus for practising the method according to claim 1 utilizing an electrically heated climate sensing body the teπperature of which is determined by a tsmperature sensor (D1) characteri zed in that a transistor (T1) is utilized and that by the current (I) caused power decipation is used for the purpose of heating the climate sensing body, a resistor (R) is utilized for the simulation of the thermal resistance of the skin and wall respectively and that a voltage divider (R2-R3) is utilized for the simulation of the human body temperature or the inner surface temperature of the wall by a proportional electric potential (U_b).

4. Apparatus according to claim 3 c h a r a c t e r i z e d in that for the control of the voltage drop across the resistor (R) an operational amplifier is utilized so that the intended function of the potentials (U_b) and (U_s) is achieved.

5. Apparatus according to claim 3 or 4 characteri z ed in that for the simulation of the human perspiration the climate sensing body is so designed that water may evaporate from its surface.

6. Apparatus according to claim 3 or 4 character i z ed in that for the control of the influence of air movements on the climate sensing body a suitable designed shield is included.