Method and arrangement for controlling heat transfer in ventilat

Details Method and arrangement for controlling heat transfer in ventilat Method and arrangement for controlling heat transfer in ventilat

1996-04-30

1998-09-15

Ford, John K.

Heat exchange

With alarm, indicator, signal, register, recorder, test or...

165 54, 165295, 165293, 165 66, 165252, 16510431, 165909, 62 95, F25B 2900, F24F 300, F24F 1100

Patent

active

058065822

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a method for controlling heat transfer in a ventilation apparatus or an air conditioning apparatus, according to which method heat transfer circuit based on fluid circulation, transfer circuit when the heat transfer is insufficient for maintaining a desired temperature of the supply air, and to achieve a desired temperature of the supply air.
In air conditioning systems, recovery of heat from outlet air exhausted from a building, i.e. exhaust air, into inlet air supplied to the building from outdoors, i.e. supply air, has become common. Heat exchangers operating on a number of different principles have been designed for heat recovery. A very common type is a plate heat exchanger in which heat is transferred through a wall from the exhaust air to the supply air as the exhaust and supply air flow in adjacent passages separated by plate walls. Almost as common is what is known as the regenerative heat exchanger in which the heat in the exhaust air is bound to a solid heat carrier that is brought to the supply air flow, whereupon said carrier gives up the bound heat. Most commonly this solid carrier is built as a rotatable drum through one half of which the exhaust air flows and through the other half of which the supply air flows.
Optimization of operation does not constitute a problem with either of these heat exchanger types. Their power can only be controlled with partial load, i.e. when the heat flow that can be recovered from the exhaust air exceeds the heat flow needed for heating the supply air. The power of plate heat exchangers is most often cut down by conducting part of the supply and/or exhaust air flow past the heat exchanger. Also regenerative recovery can be produced by means of bypass control, yet in most by controlling the speed of rotation of the drum. When the speed of rotation decreases, the heat output is reduced. Neither of these heat exchanger types can be controlled after the heating demand of the supply air exceeds the heat flow recovered from the exhaust air. The temperature control of the supply air is performed by adjusting the power of a separate after-heating radiator.
On the other hand, in a fluid circulation system consisting of separate heat exchangers in the supply air flow and the exhaust air flow and a pipeline system in between, wherein a circulation pump circulates a heat carrier fluid in a closed circuit, control is necessary to optimize the operation. Also in this case, control of the final temperature of the supply air is performed by adjusting the power of a separate after-heating radiator.
This control method is simple and, furthermore, a considerable part of the heat content in the exhaust air can be transferred to the supply air when the temperature changes of the supply and exhaust air are equal, in other words, in terms of the denotations of FIG. 1, T.sub.e1 -T.sub.e2 =.DELTA.T.sub.e =.DELTA.T.sub.s =T.sub.s2 -T.sub.s1. In that connection, the temperature efficiency, defined as follows ##EQU1## is adequate in most practical cases.
In practice, the control is performed by conducting part of the fluid flow circulated by the pump in a closed pipeline system past the heat exchanger for supply air or the heat exchanger for exhaust air by means of a valve.
It has been possible to demonstrate by way of calculation examples that the maximum value of temperature efficiency is actually achieved only at one point of the control range, especially when phase changes, usually condensation of water, occur. Yet by this simple rule-of-thumb the operation can be controlled and assumes the correct direction; therefore this principle is generally followed in designing the control logic.
However, the method is attended by essential drawbacks. In fact, this method controls the fluid flow passing through the supply air heat exchanger in response to the temperatures of the supply air flow and exhaust air flow with no information on the result of the control, i.e. on what the fluid flow passing through the supply air heat exch

REFERENCES:
patent: 5573058 (1996-11-01), Rolin

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