17
The more turbulent the air flow in the duct (evaluated by
broad deviations between one measurement and the
next) the denser the meshes in the sampling grid will be.
The REFERENCE MEASUREMENT is the arithmetic mean
of the measurements taken.
Using a REVOLVING-VANE ANEMOMETER a series of
VELOCITY MEASUREMENTS must be taken on the
external air intakes (if the Unit is configured for outside
air only) or at the intake grilles or delivery inlets.
The revolving-vane anemometer is not reliable for
measurements related to anemostatic or high-induction
diffusers.
The revolving-vane anemometer is recommended when
measurements are taken on a maximum of 2 or 3 intake
grilles so as to avoid summing together measurement
errors that would lead to an unacceptable calculation of
the hourly flow. It is therefore clear that, for
measurements on 4 or more diffusion inlets, the
reliability of the measurement is compromised and may
only be used as an approximate reference or as a rough
check on more accurate measurements made at one or
two positions on the intake duct
- The TCF Technical Department recommends you
double-check the flow rate results obtained as described
above, using the characteristic curve of the fan wheel
used (graph 1 shows an example):
- identify the curve corresponding to the fan's rpm.
- identify the curve corresponding to the absorbed power
at the shaft (P), previously calculated using the formula:
GRAPH 1
The CURRENT INTENSITY measurement of the fan motor
units under operating conditions should be made on the
remote control power switches inside the control board,
using an amperometer clamp.
Under no circumstances must the measurements be made
directly on the motor terminals since this is possible only
with the inspection door open, a condition that would
alter the length of the air circuit and therefore the
working point of the fans.
- Descend vertically from the point of intersection of the
power and rpm curves to obtain the FLOWRATE value on
the x-axes.
5.2.3. Checking heat exchanger efficiency
Check the EFFICIENCY OF THE HEAT EXCHANGERS by
measuring the temperature of the air and the carrier fluid
at the inlet and outlet with temperature gauges fitted with
telescopic contact probe. These measurements may be
made only after you have checked:
- correct connection to the distribution circuits (section
4.2.
- complete de-aeration of the circuits
- compliance of fluid temperature values with the design
values
- proper operation of the electronic adjustment
- correct opening and closing of the mixing valves and the
other exchanger control devices installed (diverter and
check valves, ON/OFF or modulating servomotors on air
locks, etc).
The AIR TEMPERATURE MEASUREMENTS must be made
with a telescopic temperature gauge through holes made
in the unit ducts or panels upstream and down-stream of
the exchangers to be checked.
The sensitive element of the temperature gauge must be
placed inside the duct or the Unit so that it is directly in
the path of the air flow, avoiding "dead zones" (e.g. by the
walls on the heat exchanger manifolds) which would
falsify the measurements (fig. 34).
On completion of the operation CLOSE THE HOLES made
with plugs.
