GB2171791A - Heating and ventilating system - Google Patents

Abstract

A heating and ventilating system especially for buildings such as churches which require infrequent, short term heating, comprises ducting 1 extending from an inlet 3 arranged to receive air from outside the building to an outlet 4 arranged to deliver air into the building. A fan 5 in the ducting supplies air to a burner 6 in the ducting which heats the air passing to the outlet via a sound attenuator 8. A control system regulates the heat output of the burner by reducing the fuel supply to the burner when the temperature is below a pre-set value, thereby reducing thermal shock caused by heating the building too rapidly. <IMAGE>

Description

SPECIFICATION Heating and ventilating system This invention relates to a heating and ventilating system.

There are traditional problems associated with heating large-volume spaces in buildings such as churches, and especially such buildings which are used only infrequently and for short periods. Conventional heating systems employ heat-exchangers for transferring heat from piped hot water to the atmosphere, but this is inefficient and does not provide ventilation for the building. Further, considerable time may be required to build up the temperature throughout the building, as stratification occurs wherein the heat rises to the upper levels where it is not needed.

According to the present invention there is provided a heating and ventilating system comprising ducting extending from an inlet arranged to receive air from outside a building to an outlet arranged to deliver air into the building, a fan in the ducting for moving air from the inlet to the outlet, and a burner in the ducting for directly heating air passing from the inlet to the outlet.

In some cases, especially where the building is for example a church of considerable age, rapid heating can cause damage to the fabric of the structure. The system of this invention can be modified to deal with such situations by connecting to the burner control means which senses the temperature of the building and the time available for heating it to its desired temperature. The control means can then actuate the burner at a reduced fuel flow until the building is warmed, whereupon the fuel flow is increased to achieve the desired temperature at the required time. This gradual heating pattern can reduce thermal shock damage to the building.

The control means may be an optimiser connected electrically to temperature sensors.

Preferably such sensors are provided to detect the temperature (a) external of the building (b) internal of the building and (c) within the ducting downstream of the burner.

The optimiser may be a conventional apparatus which controls the entire heating time and temperature range itself, or it may be allied to a thermostat which actuates a valve within the fuel flow line to increase or decrease the rate of fuel feed to the burner in response to ambient temperature within the building. Thus the optimiser can control the time of actuation of the burner and the final temperature to be achieved in the time availabie, while the thermostat can control the rate of temperature increase during the early stages of heating.

The ducting is preferably modular in construction and capable of being assembled to provide a non-linear flow path, so that it can be accommodated into a wide range of shapes and sizes of available spaces; this can be very useful in installations in old churches.

Preferably one or more silencers in the form of attenuators are included in the ducting to reduce the noise level at the outlet.

The burner is preferably fuelled by gas, for example natural gas or LPG.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic side view of a heating and ventilating system of this invention; Fig. 2 is a flow chart showing the operation of control means for the system of Fig. 1; and Fig. 3 is an exploded side view of part of a heating and ventilating system of this invention.

Referring to the drawings, a basic heating and ventilating system of the invention has ducting 1 which is contructed from short square-section tubular sections 2 having end flanges through which the adjacent sections are bolted to one another. The ducting 1 extends from an inlet at a grill 3 in an outside wall of an old church to an outlet at a grill 4 in an.internal wall leading to the main chamber of the church. A rotary fan 5 is mounted in the ducting 1 to provide air flow from the inlet grill 3 to the outlet grill 4. The fan 5 is electrically driven.

Downstream of the fan 5 is a direct-fired natural-gas burner 6 fed through a gas line 7.

The burner 6 is shaped so that air from the fan 5 flows over it in a manner which contains the flame and prevents it being entrained in the air flow, while being directed so as to provide effective direct heat transfer to the air flow.

A series of attenuators 8 are disposed downstream of the burner 6 to act as silencers. The attenuators 8 have V-shaped inlets 9 to divide the air flow and create turbulence, and are then parallel-walled and lined with sound-absorbing material 10 so that the turbulent flow is effectively sound deadened.

Referring particularly to Fig. 2, the control system for the burner 6 includes an optimiser 11 electrically connected to a series of three temperature detectors 12, 13, 14. The detector 12 is a space detector located within the church and indicating to the optimiser 11 the ambient temperature of the space to be heated; the detector 13 is located in the ducting 1 at the outlet grill 4 to indicate the temperature of the heated air being introduced into the space to be heated; and the detector 14 is located outside the church to indicate the external air temperature.

The optimiser 11 is electrically connected directly, in a first mode of the system, to a regulating valve 15 which controls a valve member 16 in the gas line 7 for the burner 6.

In an alternative mode the optimiser 11 is connected to the regulating valve 15 through an electric circuit 17 which "inverts" the optimiser 11 signal for a percentage of the ''warm-up'' time.

In use, the optimiser 11 learns its environment over a period of, say, three days. Using resistance values from the detectors 12, 13, 14 it adjusts the switch-on time of the fan 5 and burner 6 to reach a predetermined temperature by a certain time, regardless of heat losses from the building or supply air temperature. Using the output to the valve 15 to control directly the flow of gas to the burner 6, as the temperature of the space to be heated rises to a preset level, the supply of gas to the burner 6 is reduced to a level where the supply air temperature and volume provide a heat input of the required amount to offset the heat losses and keep the space temperature at the required level. This is the first mode of operation.

In the second mode the optimiser 11 signal is inverted by the circuit 17 and the inverted signal fed to the valve 15 for 50% of the heating time. With the optimiser 11 calling for full gas flow to the burner 6, therefore, the signal reaching the valve 15 reflects a reduced flow until the timing sequence in the circuit 17 requires the valve 15 to revert to a natural response to the signal from the optimiser 11.

This second mode reduces the thermal shock on heating a building, and is especially useful in buildings such as old churches which require effective but short-term heating. The fan 5 on actuation draws cold fresh air into the ducting 1 through the grill 3, the air flow is heated in the burner 6 and sound-reduced in the attentuators 8, and blown through the grill 4 into the space to be heated. The use of external air results in a positive pressure within the building, so that heated air leaks out under doors and around windows; eliminating draughts.

Further details of the heating and ventilating system control operation will now be described. The system employs a change over thermostat which is linked to the main gas modulating valve to prevent it opening beyond a predetermined amount when the room temperature is below the chosen change over temperature. A frost thermostat is also employed and its function is to bring the system into operation when the room temperature falls below a certain level.

The operation of the system is such that the heating of the premises is kept at a low level below the change over temperature.

For example, if the changeover thermostat is set to 10 C, the main gas modulating valve opening set to 30 degrees and the frost thermostat set to 5"C the operation of the system will be as follows. When the room temperature drops below 5"C the system will switch on. However, the changeover thermostat effectively overrides the other system's demands for a high heat output and allows the main gas modulating valve to open only to the predetermined setting of 30 degrees. This has the effect of limiting the heat output of the system to approximately one third of the rated capacity so that the rise in room temperature is relatively slow thus reducing thermal shock to the building structure.

When the room temperature reaches the changeover temperature of 10"C the changeover thermostat switches out of the control system and allows the main temperature controller to take full command of the gas modulating valve. The system thus adjusts to produce a heat output most appropriate for heating the space economically.

When the desired room temperature is reached the gas modulating valve turns down to the desired level to maintain the temperature.

After each operation the various controls reset automatically.

As a further refinement a maximum limitation control is included to ensure that the temperature of the outlet flow does not exceed 40"C if, for example, there should be an upward variation in mains gas pressure.

The system is also designed so that at the end of a heating cycle or series of heating cycles an electronic timer continues to operate the fan after the burner has shut down to effect a post heating purge of the building.

The electronic timer can be adjusted to run the fans for a long enough period to effect a complete change of air in the building and thus ensure that any residual products of combustion are removed.

Various additions, alternatives and improvements to the basic system are possible.

The basic system is designed to heat only outdoor fresh air but partial recirculation can be included if arrangements are made to ensure fresh air entry only across the burner.

The system is modular in construction (Fig.

3) with the various ductings containing the fans, burners, etc. being identical in outer dimensions and having common mountings at either end, so that any one part of the system can be joined to any other part of the system.

Modifications and improvements may be made without departing from the scope of the invention.

Claims (9)

1. A heating and ventilating system comprising ducting extending from an inlet arranged to receive air from outside a building to an outlet arranged to deliver air into the building, a fan in the ducting for moving air from the inlet to the outlet, and a burner in the ducting for directly heating air passing from the inlet to the outlet.

2. A heating and ventilating system as claimed in Claim 1, wherein temperature sensors are provided for determining the tempera ture external of the building, internal of the building, and within the ducting downstream of the burner.

3. A heating and ventilating system as claimed in Claim 1 or 2, wherein means are included for limiting the heat output of the burner when the interior of the building is below a pre-determined level.

4. A heating and ventilating system as claimed in Claim 1, 2 or 3, wherein control means are included which may be preprogrammed with data relating to the rate of temperature increase in the interior of the building on operation of the system such that the control means may ascertain a start up time for the system for achieving a desired interior temperature at a desired time.

5. A heating and ventilating system as claimed in any one of the preceding Claims, wherein means are included which serve to cause the system to commence operating at a low level if the interior temperature drops below a predetermined level.

6. A heating and ventilating system as claimed in any one of the preceding Claims, wherein means are included to prevent the temperature of the air in the ducting downstream of the burner exceeding a pre-determined level.

7. A heating and ventilating system as claimed in any one of the preceding Claims, wherein the ducting is modular in construction with the various ductings for air passage and those containing the fans and burners being identical in outer dimensions and having common mountings at either end so that any combination of parts may be joined together to form the system.

8. A heating and ventilating system as claimed in any one of the preceding Claims, wherein timer means are included which continue to operate the fan for a limited period after the burner has shut down.

9. A heating and ventilating system substantially as hereinbefore described with reference to the accompanying drawings.