Sharp JX-9400 Informazioni Techniche Scaricare il pdf (Pagina 104)

From the indoor env ironment, heat loads and solar gains. This way ,

common in tropical climates, saves the investment of the heating system,

and heating energy is free. It has, however, the disadvantage of blowing

cold air into the occupied spaces, often leading to draughts. In such systems,

recirculation is often very large and temperature control is obtained by

varying the supply airﬂow rate.

Heat provided to a warm heat exchanger by the heat pump used to cool down

the chil led water. This heat pump provides cooling water at temperatures

higher than indoor temperature. This water or a part of it can be circulated

into the warm heat exchanger without any running cost. The investment is

limited to pipes connecting the chiller condenser to the warm heat exchanger

and to a control valve.

Heat provided to a warm heat exchanger by a separate heating system. This

is expensive both in investment and running costs and should not be used.

Measurement of energy for heating, cooling, humidifying or

dehumidifying air

The amount of energy needed to increase the temperature and hum idity of a

known volume of air depends only on the start and ﬁnal values of temperature

and humidity ratios. Using Equation 5.1:

Q ¼ hV ¼ Vc

 þðL þ c

Þx ð5:3Þ

Therefore, measuring the airﬂow rate (according to Chapter 2, ‘Measurement

of airﬂow in a duct’) through the heating coils and humidiﬁer (if any), as well as

air temperature and moisture upwind and downwind of these elements, allows

for the calculation of the heating and humidifying power.

This is not that simple for cooling and dehumidifying. The measurement of

airﬂow rate is the same, but air temperature and humidity should be measured

before and after each of the processes mentioned in Table 5.1:

Cooling and dehumidiﬁcation – measurements in outdoor air and after the

cooling coils provide the power taken from the chilled water. This power

may also be obtained by measuring the chilled water ﬂow rate in the cooling

coil and its temperature increase.

Reheating – measurements before and after the heating coil give the power

provided by the reheating system. This power can also be calculated from

measurements of the heating water ﬂow rate in the heating coil and its

temperature decrease.

Heat exchangers

The purpose of heat exchangers is to transfer heat from water to air (heating

coils) or vice versa (cooling coils). This heat should be transferred in the

most eﬃcient way possible, without transferring contaminants. The diagnosis

should characterize the performance of the exchanger.

Measurements and Measures Related to Energy Eﬃciency in Ventilation 83

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