SE2150351A1 - Ventilation equipment and method of operating ventilation equipment - Google Patents

Abstract

Ventilation equipment comprises a supply convector (10), a supply fan (18) for conducting supply air through the supply convector (10), an exhaust convector (12), an exhaust fan (20) for conducting exhaust air through the exhaust convector (12), and a heat transfer pipework having a first pipe (24) from the supply convector to the exhaust convector, a second pipe (26) from the exhaust convector to the supply convector, an intermediate pipe (25) from the first pipe to the second pipe, a circulating pump (34), and at least one valve (28). The equipment also comprises a control device (32) for controlling the operation of the supply and exhaust fans, valve and circulating pump, and pressure measuring means (36a, 36a) for measuring the pressure difference across the exhaust convector. The valve is a three-way valve and the flow of heat transfer fluid in the heat transfer pipework can be divided by the valve into a first part flowing through the supply convector and a second part flowing simultaneously past the supply convector.

Description

Ventilation equipment and method of operating ventilation equipment FIELD OF THE INVENTION The invention relates to ventilation equipment comprising a supply convector, asupply fan for conducting supply air through the supply convector, an exhaustconvector, an exhaust fan for conducting exhaust air through the exhaustconvector, a heat transfer pipework, wherein the heat transfer pipework has a firstpipe leading from the supply convector to the exhaust convector, a second pipeleading from the exhaust convector to the supply convector, an intermediate pipeleading from the first pipe to the second pipe, a circulating pump and at least onevalve, a control device for controlling the operation of said supply and exhaustfans, said at least one valve and said circulating pump, and a pressure measuringmeans for measuring the pressure difference across the exhaust convector. Theinvention also relates to a method for operating the ventilation equipment.

PRIOR ART The energy efficiency of ventilation systems is improved by heat recoveryequipment, which preheats the incoming supply air with thermal energy recoveredfrom the exhaust air. Especially in large buildings, ventilation systems are usedwhich have an exhaust convector through which the exhaust air is blown bymeans of an exhaust fan and a supply convector through which the supply air issucked by means of a supply fan. The supply convector and the exhaustconvector are connected to each other by heat transfer pipework so that the heattransfer fluid heated by the exhaust air is led from the exhaust convector to thesupply convector, where it heats the supply airflow. From the supply convector thecooled heat transfer fluid returns to the exhaust convector. The heat transfer fluidused in the ventilation equipment described above is typically a glycol or anaqueous glycol solution.

There are several problems with known ventilation equipment. Moisture in theexhaust air condenses and easily builds up frost on the lamellae of the exhaustconvectors, which reduces the amount of air passing through the convector anddegrades the heat transfer capacity of the convector, reducing the heat recoveryefficiency. ln conventional ventilation equipment, an attempt is made to preventthe build-up of frost in the exhaust convector by setting a lower limit for thetemperature of the heat transfer fluid, below which the heat transfer fluid is notallowed to cool. Typically, the lower limit for the temperature is between -5°C and 0°C. When the temperature of the heat transfer fluid drops to the lower limit, theflow of heat transfer fluid through the supply convector is reduced. The speeds ofthe inlet and exhaust fans are normally not changed during the anti-frost operation.

The temperature of the heat transfer fluid alone does not reliably indicate whetherthe |ame||ae of the exhaust convector are actually building up frost, so raising thetemperature of the heat transfer fluid is often carried out unnecessarily. Thedeterioration of the heat recovery efficiency is further exacerbated by the fact thatthe lower limit for the temperature of the heat transfer fluid is often setunnecessarily high for fear of build-up of frost in the exhaust convector. Thecirculation of the heat transfer fluid due to anti-frost operation is regulated the mostat low outdoor temperatures, when the heat output provided by the heat recoveryfunction would be needed the most.

The speed of the circulating pumps in the ventilation equipment is adjusted duringthe installation phase of the equipment so as to achieve the designed heat transferfluid flow rate in the fluid circulation loop. During operation of the equipment, theflow rate of the heat transfer fluid is not measured or adjusted in any way.However, the viscosity of the glycol-containing heat transfer fluid depends greatlyon the temperature of the fluid, which is why the flow of the heat transfer fluidduring operation of the equipment differs significantly from the flow rate set duringthe installation phase. The circulating pumps run at the same constant speed,which results in too low a flow rate and a low heat recovery efficiency, especially inwinter. During summer, on the other hand, a lower speed would suffice to providesufficient flow in the pipework. A circulating pump running at excessive speedconsumes an unnecessary amount of energy.

EP2910866 discloses a ventilation system with at least two exhaust convectorsarranged in the exhaust air flow and at least two supply convectors arranged in thesupply air flow. The circulation of the heat transfer fluid through at least one othersupply convector can be stopped momentarily, but the heat transfer fluid mustalways circulate through at least one other supply convector. ln this solution,several convectors are arranged in the supply and exhaust air flows, throughwhich the air is made to flow, which makes the equipment structurally complex andexpensive.

Fl 20165247 describes ventilation equipment comprising a supply convector, anexhaust convector and a pressure measuring means for measuring the pressuredifference across the exhaust convector. The publication discloses a solution where the flow rate of the heat transfer fluid through the supply and exhaustconvectors is to be kept substantially constant by adjusting the rotational speed ofthe circulating pump. A constant heat transfer fluid flow rate improves the heatrecovery efficiency of the equipment. Build-up of frost in the supply convector ismonitored by continuously measuring the pressure difference across the supplyconvector. A control device in the equipment is arranged to cut off the flow of heattransfer fluid through the supply convector completely for a period of time whenthe measured pressure difference across the supply convector exceeds a set limitvalue.

The weakness of this solution, which works well per se, is that the length and flowresistance of the heat transfer pipework change abruptly when the flow throughthe supply convector is completely cut off, which makes it difficult to regulate theflow rate of the heat transfer fluid in a controlled manner.

An object of the invention is to provide ventilation equipment and a method ofoperating ventilation equipment, with which the problems related to the prior artcan be reduced. The objects of the invention are achieved by ventilationequipment and a method which are characterized by what is set out in theindependent claims. Some preferred embodiments of the invention are set out inthe dependent claims.

SUMMARY OF THE INVENTION The invention relates to ventilation equipment comprising a supply convector, asupply fan for conducting supply air through the supply convector, an exhaustconvector, an exhaust fan for conducting exhaust air through the exhaustconvector, and a heat transfer pipework. The heat transfer pipework has a firstpipe leading from the supply convector to the exhaust convector, a second pipeleading from the exhaust convector to the supply convector, an intermediate pipeleading from the first pipe to the second pipe, a circulating pump and at least onevalve. The equipment also comprises a control device for controlling the operationof said supply and exhaust fans, said at least one valve and said circulating pump,and a pressure measuring means for measuring the pressure difference acrossthe exhaust convector. The valve in the heat transfer pipework is a three-wayvalve and the flow of heat transfer fluid in the heat transfer pipework can bedivided by the valve into a first part flowing through the supply convector and a second part flowing simultaneously past the supply convector. Preferably, saidvalve is at the junction of the first pipe and the intermediate pipe. ln a preferred embodiment of the ventilation equipment according to the invention,said valve is steplessly adjustable between a first position in which substantially100% of the heat transfer fluid is directed to flow through the supply convector,and a second position in which substantially 100% of the heat transfer fluid isdirected to flow past the supply convector.

Another preferred embodiment of the ventilation equipment according to theinvention further comprises cooling means for lowering the temperature of the heattransfer fluid flowing in the heat transfer pipework. Preferably, said cooling meanscomprises a cooling machine, a supply pipe leading from the cooling machine tothe second pipe and a return pipe leading from the first pipe to the coolingmachine, and a distribution valve. Said distribution valve may be at the junction ofthe first pipe and the return pipe.

The invention further relates to a method for controlling the operation of ventilationequipment, which ventilation equipment comprises a supply convector, a supplyfan for conducting supply air through the supply convector, an exhaust convector,an exhaust fan for conducting exhaust air through the exhaust convector, a heattransfer pipework, wherein the heat transfer pipework has a first pipe leading fromthe supply convector to the exhaust convector, a second pipe leading from theexhaust convector to the supply convector, an intermediate pipe leading from thefirst pipe to the second pipe, a circulating pump and at least one valve, a controldevice for controlling the operation of said supply and exhaust fans, said at leastone valve and said circulating pump, and a pressure measuring means formeasuring the pressure difference across the exhaust convector. The methodcomprises adjusting the rotational speed of the circulating pump to an optimumspeed which is substantially lower than the maximum speed, dividing the flow ofheat transfer fluid by means of a valve into a first part flowing through the supplyconvector and a second part flowing simultaneously past the supply convector andas the need for heating supply air increases, increasing the first part flowingthrough the supply convector and, as the need for heating supply air decreases,decreasing the first part flowing through the supply convector. The optimum speedof the circulating pump is the lowest speed at which sufficient circulation of heattransfer fluid is achieved in the heat transfer pipework on most days of operation ofthe ventilation equipment. ln a preferred embodiment of the method according to the invention, aftersubstantially 100% of the heat transfer fluid has been directed to flow through thesupply convector, as the need for heating supply air increases, the circulatingpump speed is increased above the optimum speed and, as the need for heatingsupply air decreases, the circulating pump speed is decreased toward theoptimum speed. Thus, the speed of the circulating pump is only increased abovethe optimum speed when the heat transfer of the supply convector can no longerbe made more efficient by adjusting the valve.

Another preferred embodiment of the method according to the invention comprisessetting a limit value for the pressure difference across the exhaust convector,measuring the pressure difference across the exhaust convector substantiallycontinuously and, when the measured pressure difference exceeds the set limitvalue, reducing the flow of heat transfer fluid through the supply convector for aperiod of time and reverting to the level preceding the reduction after the periodhas elapsed. Preferably, the flow of heat transfer fluid through the supplyconvector is reduced by more than 50%, preferably by more than 70%, mostpreferably by 90% from the pre-reduction level.

Another preferred embodiment of the method according to the invention comprisesdetermining the critical temperature for the solidification of the heat transfer fluid,measuring the temperature of the heat transfer fluid flowing in the heat transferpipework, comparing the measured temperature with the critical temperature forthe solidification of the heat transfer fluid, and reducing the flow of heat transferfluid through the supply convector when the measured temperature is lower thanthe critical temperature.

Another preferred embodiment of the method according to the invention comprisescutting off, if necessary, the flow of heat transfer fluid through the exhaustconvector and cooling the supply air flow by lowering the temperature of heattransfer fluid flowing through the supply convector by cooling means. Preferably,the method comprises directing heat transfer fluid from the first pipe to a coolingmachine, chilling the coolant in the cooling machine, directing the chilled coolantfrom the cooling machine to the second pipe, and as the need for cooling supplyair increases, increasing the first part flowing through the supply convector and, asthe need for cooling supply air decreases, decreasing the first part flowing throughthe supply convector by regulating the valve.

An advantage of the invention is that the flow of heat transfer fluid in the heattransfer pipework largely takes place continuously at the same, optimal speed,which improves the heat recovery efficiency. The heat recovery efficiency is alsoimproved by the fact that the circulation of heat transfer fluid through the supplyconvector is only restricted when there is a real risk of a build-up of frost.

Another advantage of the invention is that running the circulating pump at theoptimum speed saves energy.

Yet another advantage of the invention is that the equipment is structurally simpleand inexpensive to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in detail below. The description refers to theaccompanying drawing, in which Fig.1 shows by way of example ventilation equipment according to theinvention in a schematic view.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows by way of example ventilation equipment according to the inventionin a simplified schematic view. The ventilation equipment includes a supplyconvector 10 arranged in the supply air flow 14 flowing in the ventilation ductworkof a building 100, and an exhaust convector 12 arranged in the exhaust air flow16. ln the supply air flow there is also a supply fan 18, which sucks supply air fromoutside the building into the building along a supply duct so that the supply airflows through the supply convector. The supply fan is placed in the supply ductafter the supply convector with reference to the supply air flow direction.Correspondingly, there is in the exhaust air flow 16 an exhaust fan 20 by means ofwhich exhaust air is blown from inside the building to the outside of the buildingalong an exhaust duct so that the exhaust air flows through the exhaust convector12. The exhaust fan is placed in the exhaust duct before the exhaust convectorwith reference to the exhaust air flow direction. The inlet and exhaust convectorsare liquid-circulating convectors with a flow pipework inside, with a first pipeconnection 22a at a first end and a second pipe connection 22b at a second end.On the outer surface of the flow pipework there are lamellae that contribute to theheat transfer between the air flowing through the convectors and the heat transferfluid flowing in the flow pipework. The supply convector 10 is a so-called hybrid convector which can serve both as a heating device and a cooling device for theflowing air, depending on the temperature of the heat transfer fluid led into the flowpipework of the convector. The supply and exhaust convectors as such are knownin the art, so their structure will not be described in more detail here.

The first pipe connection 22a of the supply convector is connected by a first pipe24 to the first pipe connection 22a of the exhaust convector 12, and the secondpipe connection 22b of the supply convector is connected by a second pipe 26 tothe second pipe connection 22b of the exhaust convector 12 so as to form a heattransfer fluid flow path through the supply and exhaust convectors. The first andsecond pipes are connected to each other by an intermediate pipe 25. At thejunction of the first pipe and the intermediate pipe there is a valve 28. The valve isa so-called 3-way valve with an actuator, the opening and closing of which iscontrolled by a control device 32. The valve can be used to restrict or completelycut off the flow of heat transfer fluid to a pipe of the heat transfer pipeworkconnected to the valve. The valve 28 has a flow meter to measure the flow of heattransfer fluid in the pipes connected to the valve. The second pipe 26 has acirculating pump 34 for circulating the heat transfer fluid in the pipes andconvectors. The heat transfer fluid used in the ventilation equipment is typicallyglycol, an aqueous solution of glycol or a mixture of ethylene glycol. The speed ofthe circulating pump is controlled by a frequency converter 35. The valve, thecirculating pump and the frequency converter are connected by wires to thecontrol device 32 which controls their operation. ln the exhaust air flow 16, on a first and second sides of the exhaust convector 12there are respectively a first pressure sensor 36a and a second pressure sensor36b for measuring the exhaust air pressure on the different sides of the exhaustconvector. The pressure sensors are connected by wires to the control device 32.The inlet and exhaust fans 18, 20 are also connected by wires to the controldevice which controls the operation of the fans.

The ventilation equipment according to the invention further comprises coolingmeans for cooling the supply air flow. The cooling means comprises a coolingmachine 40, a supply pipe 42 leading from the cooling machine to the second pipe26, and a return pipe 44 leading from the first pipe 24 to the cooling machine. Thesupply pipe connects to the second pipe in the section between the exhaustconvector 12 and the circulating pump 34, and the return pipe connects to the firstpipe in the section between the valve 28 and the exhaust convector. At thejunction of the return pipe and the first pipe, there is a distribution valve 46 for controlling the amount of heat transfer fluid flowing from the first pipe to the returnpipe. The amount of coolant flowing in the return pipe is equal to the amount ofheat transfer fluid flowing in the supply pipe, so the distribution valve also controlsthe amount of cooled heat transfer fluid flowing into the supply pipe. Thedistribution valve is a 3-way valve with an actuator, known per se, the operation ofwhich is controlled by the control device 32.

The equipment further includes three thermometers to measure the temperature ofthe heat transfer fluid flowing in the heat transfer pipework. The first thermometer48a is in the first pipe 24, in the section between the supply convector 10 and thevalve 28, the second thermometer 48b is in the first pipe, in the section betweenthe distribution valve 46 and the exhaust convector 12, and the third thermometer48c is in the second pipe 26, in the section between the circulating pump 34 andthe supply convector 10.

The control device 32 included in the ventilation equipment is a control unit knownper se with programmable logic, with a possibility of connecting to a buildingautomation system through connections in the control device. The control devicehousing has a main switch and a graphic touch screen, which can be used to setparameters that control the operation of the equipment and to view quantitiesmeasured by the meters in the equipment. The control device can be connected toa remote control device outside the building, such as a computer or mobile phone,through a wired or wireless communication connection 102.

The ventilation equipment according to the invention is operated in the followingway: When the ventilation equipment is in the normal operating mode, the supplyand exhaust fans are running, whereby the supply air flows along the supply ductthrough the supply convector 10 inside the building 100, and the exhaust air flowsalong the exhaust duct through the exhaust convector 12 outside the building. lfthe temperature of the supply air flow 14 flowing through the supply convector issuitable, i.e. it does not need to be heated or cooled, the circulating pump 34 canbe switched off, whereby no heat transfer fluid flows in the heat transfer pipeworkat all. The control device then controls the valve 28 to the “open” position, wherebythe valve branch connected to the intermediate pipe 25 is closed.

An upper and lower limit for the temperature of the supply air flow 14 can be set inthe control device 32. When the supply air flow temperature falls below the lowerlimit, i.e. there is a need to heat the air flowing through the supply convector, thecontrol device 32 starts the circulating pump and adjusts its rotational speed to a preset minimum rotational speed. Information about the need for heating thesupply air can also come from a building automation system connected to thecontrol device, which monitors, among other things, the indoor temperature in thebuilding. Based on the supply air flow heating need, the control device calculatesthe required flow through the supply convector and steplessly adjusts the valve 28so that a first portion of the heat transfer fluid flows through the supply convector10, heating the air flowing through the supply convector, and a second portion ofthe heat transfer fluid flows through the intermediate pipe 25, bypassing the supplyconvector. As the need for heating the supply air flow increases, the first portion isincreased and the second portion is reduced until the valve 28 is fully open, so thatall the heat transfer fluid flowing in the heat transfer pipework flows through boththe supply convector and exhaust convector 12, and no heat transfer fluid flows inthe intermediate pipe 25 at all.

When the supply air temperature falls low enough, the need for heating the supplyair flow increases to such an extent that the required flow through the supplyconvector is not achieved despite all heat transfer fluid being directed to flowthrough the supply convector. ln this case, the control device increases therotational speed of the circulating pump 34 by means of the frequency converter35 so that a sufficient flow of heat transfer fluid is achieved. The speed of thecirculating pump can be steplessly adjusted to achieve the required flow rate.

When the need for heating the supply air flow decreases, the operation isreversed, i.e. the speed of the circulating pump is first reduced to the minimumspeed, after which the amount of heat transfer fluid flowing through the supplyconvector is limited by the valve 28.

During the operation of the ventilation equipment according to the invention,pressure sensors 36a, 36b continuously measure the pressure difference acrossthe exhaust convector 12 in the exhaust air flow 16. A limit value for the pressuredifference is preset in the control device 32 of the ventilation equipment. The limitvalue refers to the maximum permissible value for the pressure difference acrossthe exhaust convector, i.e. the maximum permissible value for the difference in airpressures measured by the first and second pressure sensors. The limit value canbe adjusted and changed during operation of the equipment. Exhaust convectorshave an inherent structural pressure drop. Structural pressure drop here meansthe pressure drop caused by the exhaust convector when the exhaust convector iscompletely “clean”, i.e. there is no extra substance or material to increase the pressure drop between its lamellae. The limit value for the pressure difference canbe set to twice the value of the structural pressure drop of the exhaust convector.

When the supply air temperature decreases, the temperature of the heat transferfluid decreases in the supply convector, whereby heat transfer fluid flowing into theexhaust convector is cooler. A sufficiently low temperature of the heat transfer fluidmakes the surfaces of the lamellae of the exhaust convector so cold that moisturein the exhaust air begins to condense on them, i.e. the lamellae begin toaccumulate frost. The build-up of frost on the lamellae results in an increase in thepressure difference across the exhaust convector. When the measured pressuredifference reaches the set limit value, the ventilation equipment enters a so-calleddefrost mode, whereby the control device 32 adjusts the valve 28 so that a portionof the heat transfer fluid is directed to flow through the intermediate pipe 25 pastthe supply convector, reducing the proportion of heat transfer fluid flowing throughthe supply convector 10. ln the defrost mode, the amount of heat transfer fluidflowing through the supply convector is steplessly reduced by a desired amount.The reduction in the flow of heat transfer fluid can be, for example, more than50%, more than 70%, or even 90% from the pre-reduction level. ln principle, it ispossible to completely cut off the flow of heat transfer fluid through the supplyconvector, but the invention seeks to avoid such a situation. ln the defrost mode,the heat transfer fluid still circulates through the exhaust convector in its entirety,but due to the partial bypass of the supply convector, its temperature rises as thewarm exhaust air flow through the exhaust convector raises the temperature of theexhaust convector lamellae. At the same time, the moisture condensed on thelamellae of the exhaust convectors dries out and flows out under the influence ofthe exhaust air flowing through.

The ventilation equipment remains in the defrost mode for a pre-set period of timeset in the control device. The length of the pre-set period of time can be, forexample, 10-15 minutes. A suitable length for the pre-set period of time can beselected during operation of the equipment. At the end of the pre-set period oftime, the control device 32 returns the valve 28 to the pre-defrost mode position,whereby the ventilation equipment reverts to the normal operating mode. Theventilation equipment continuously measures the pressure difference across theexhaust convector, compares it to the set limit value and, if necessary, switchesthe equipment again to the defrost mode for a pre-set period of time. A minimuminterval can be set in the control device between successive defrost modes.

The heat transfer fluid used in the ventilation equipment is typically glycol, anaqueous solution of glycol or a mixture of ethylene glycol that solidifies at a certaintemperature. The solidification temperature depends on the composition of theheat transfer fluid. ln the ventilation equipment according to the invention, a criticaltemperature is determined for the heat transfer fluid, below which the viscosity ofthe heat transfer fluid becomes too high due to solidification. The temperature ofthe heat transfer fluid flowing into the exhaust convector is continuously measuredby the second thermometer 48b. lf the temperature of the heat transfer fluid dropsto the critical solidification temperature, the control device 32 controls the valve 28so that a greater portion of the heat transfer fluid bypasses the supply convector,thereby raising the temperature of the heat transfer fluid. The control device thusrestricts the flow of heat transfer fluid through the supply convector so that thetemperature of the heat transfer fluid does not fall below the critical temperature. lf the indoor air temperature in the building is so high that there is no need to heatthe supply air, the control unit stops the circulating pump, whereby the circulationof the heat transfer fluid in the heat transfer pipework ceases. No more heat istransferred from the exhaust convector 12 to the supply convector 10, i.e. theheating of the supply airflow ceases. Especially in spring and autumn, conditionsarise in which the outdoor air temperature of the building is lower than the indoorair temperature that is to be lowered. ln this case, the supply air, which is coolerthan the indoor air, flows through the supply convector into the building, coolingthe indoor air.

As the need for cooling increases and/or the outdoor air temperature rises, thesupply air flow can be cooled by the cooling means included in the equipment. Avalue for the maximum temperature of the supply air flow can be set in the controldevice 32, or the control device can obtain information on the cooling need fromthe building automation system connected to the control device, whereby theventilation equipment enters the cooling mode. ln the cooling mode, the controldevice starts the circulating pump and sets the distribution valve 46 to a positionwhere the flow of coolant to the exhaust convector 12 is blocked and a flow pathopens to the coolant along the return pipe 44 to the cooling machine. Chilledcoolant flows from the cooling machine along the supply pipe 42 to the secondpipe 26, whereby it flows through the supply convector 10, cooling the supply airflow. ln the cooling mode, the control device sets a set value corresponding to thecooling mode for the valve 28, i.e. a maximum flow setpoint that is substantiallydifferent from the heat recovery mode setpoint. ln the cooling mode, the control device uses the valve 28 to regulate the flow of heat transfer fluid based on thecooling need, dividing the flow into a first portion flowing through the supplyconvector 10 and a second portion flowing through an intermediate pipe,bypassing the supply convector 10. The speed of the circulating pump 34 iscontrolled by a frequency converter to maintain sufficient cooling capacity.

Some preferred embodiments of the method and equipment according to theinvention have been described above. The invention is not limited to the solutionsdescribed above, but the inventive idea can be applied in various ways within thescope set by the claims.

List of reference numbers: supply convectorexhaust convectorsupply air flowexhaust air flowsupply fanexhaust fan inlet connectionoutlet connectionfirst pipeintermediate pipesecond pipevalve control device circulating pumpfrequency converterfirst pressure sensorsecond pressure sensorcooling machineSUDDW Pipe return pipedistribution valvefirst thermometersecond thermometerthird thermometerbuilding wireless communication connection

Claims (13)

Claims

1. Ventilation equipment comprising a supply convector (10), a supply fan (18)for conducting supply air through the supply convector (10), an exhaust convector(12), an exhaust fan (20) for conducting exhaust air through the exhaust convector(12), a heat transfer pipework, wherein the heat transfer pipework has a first pipe(24) leading from the supply convector (10) to the exhaust convector (12), asecond pipe (26) leading from the exhaust convector (12) to the supply convector(10), an intermediate pipe (25) leading from the first pipe (24) to the second pipe(26), a circulating pump (34) and at least one valve (28), a control device (32) forcontrolling the operation of said supply and exhaust fans (18, 20), said at least onevalve (28) and said circulating pump (34), and pressure measuring means (36a,36a) for measuring the pressure difference across the exhaust convector (12),characterized in that said valve (28) is a three-way valve and the flow of heattransfer fluid in the heat transfer pipework can be divided by the valve (28) into afirst part flowing through the supply convector (10) and a second part flowingsimultaneously past the supply convector (10).

2. The ventilation equipment of claim 1, characterized in that said valve (28) isat the junction of the first pipe (24) and the intermediate pipe (25).

3. The ventilation equipment of claim 1 or 2, characterized in that said valve(28) is steplessly adjustable between a first position in which substantially 100% ofthe heat transfer fluid is directed to flow through the supply convector (10) and asecond position in which substantially 100% of the heat transfer fluid is directed toflow past the supply convector (10).

4. The ventilation equipment of any of claims 1-3, characterized in that itfurther comprises cooling means for lowering the temperature of the heat transferfluid flowing in the heat transfer pipework.

5. The ventilation equipment of claim 4, characterized in that said coolingmeans comprise a cooling machine (40), a supply pipe (42) leading from thecooling machine (40) to the second pipe (26), and a return pipe (44) leading fromthe first pipe (24) to the cooling machine (40), and a distribution valve (46).

6. The ventilation equipment of claim 5, characterized in that said distributionvalve (46) is at the junction of the first pipe (24) and the return pipe (44).

7. A method for controlling the operation of ventilation equipment, whichventilation equipment comprises a supply convector (10), a supply fan (18) forconducting supply air through the supply convector (10), an exhaust convector(12), an exhaust fan (20) for conducting exhaust air through the exhaust convector(12), a heat transfer pipework, wherein the heat transfer pipework has a first pipe(24) leading from the supply convector (10) to the exhaust convector (12), asecond pipe (26) leading from the exhaust convector (12) to the supply convector(10), an intermediate pipe (25) leading from the first pipe (24) to the second pipe(26), a circulating pump (34) and at least one valve (28), a control device (32) forcontrolling the operation of said supply and exhaust fans (18, 20), said at least onevalve (28) and said circulating pump (34), and pressure measuring means (36a,36a) for measuring the pressure difference across the exhaust convector (12),characterized by adjusting the rotational speed of the circulating pump (34) to an optimum speedwhich is substantially lower than the maximum speed, dividing the flow of heattransfer fluid by means of a valve (28) into a first part flowing through the supplyconvector (10) and a second part flowing simultaneously past the supply convector(10), and as the need for heating the supply air increases, increasing the first partflowing through the supply convector (10), and as need for heating the supply airdecreases, decreasing the first part flowing through the supply convector (10).

8. The method of claim 7, characterized in that, after substantially 100% of theheat transfer fluid has been directed to flow through the supply convector (10), asthe need for heating the supply air increases, the rotational speed of the circulatingpump (34) is increased above the optimum speed and, as the need for heating thesupply air decreases, the rotational speed of the circulating pump (34) isdecreased toward the optimum speed.

9. The method of claim 7 or 8, characterized by setting a limit value for thepressure difference across the exhaust convector (12), measuring the pressuredifference across the exhaust convector (12) substantially continuously and, whenthe measured pressure difference exceeds the set limit value, reducing the flow ofheat transfer fluid through the supply convector (10) for a period of time andreverting it to the level preceding the reduction after the period has elapsed.

10. The method of claim 9, characterized in that the flow of heat transfer fluidthrough the supply convector (10) is reduced by more than 50%, preferably bymore than 70%, most preferably by 90% from the pre-reduction level.

11. The method of any of claims 7-10, characterized by determining the criticaltemperature for the solidification of the heat transfer fluid, measuring thetemperature of the heat transfer fluid flowing in the heat transfer pipework,comparing the measured temperature with the critical temperature for thesolidification of the heat transfer fluid, and reducing the flow of the heat transferfluid through the supply convector (10) when the measured temperature is lowerthan the critical temperature.

12. The method of any of claims 7-11, characterized by cutting off, if necessary,the flow of the heat transfer fluid through the exhaust convector (12) and coolingthe supply air flow by lowering the temperature of the heat transfer fluid flowingthrough the supply convector (10) by cooling means.

13. The method of claim 12, characterized by directing the heat transfer fluidfrom the first pipe (24) to a cooling machine (40), chilling the coolant in the coolingmachine (40), directing the chilled coolant from the cooling machine (40) to thesecond pipe (26), and as the need for cooling the supply air increases, increasingthe first part flowing through the supply convector (10), and as the need for coolingthe supply air decreases, decreasing the first part flowing through the supplyconvector (10) by regulating the valve (28).