Typical case analysis
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Chapter XIII Typical case analysis
Case I: A user installed a number of FR125/S air duct type air conditioners and complained
about poor heating effect. Pressure measurement showed that indoor unit and outdoor unit
systems were normal without clogging or leakage, and indoor area and thermal insulation met
requirements.
Analysis: (1) The indoor unit was installed in ceiling layer of toilet with ventilating windows.
Fresh air leaked into return air so that indoor unit return air temperature in winter was lower
than 0℃; (2) Insulation on air delivery hose and static pressure box was merely 5mm thick
sticky sponge.
Solution: (1) Fabricate fresh air duct plus air damper control and seal for insulation; or block
fresh air window and cancel fresh air duct; (2) Increase air duct thermal insulation to above
15mm.
Case II: A user installed more than 10 sets of FR125/S air duct air conditioners and
complained of poor heating effect. For this reason, user installed auxiliary electric heating of
sufficient power, so that indoor air delivery temperature was as high as 52℃. However, even
at high air speed setting, air delivery was very small and room temperature was low.
Analysis: (1) Space surrounding indoor unit was small and natural return air was used.
Distance between unit return air face to obstacle was only 5cm and return air was seriously
blocked; (2) Air delivery main hose was only 0.8m long, i.e. a branch hose leading 2 lines of
right angle bends. This branch hose was 20cm diameter round corrugated plastic hose and
total air delivery cross sectional area was less than 0.1 m
2
, hence air delivery side was
seriously blocked.
Solution: (1) Reinstall indoor unit and change its orientation; also ensure certain space to
allow free air return; (2) Increase air delivery branch hose cross sectional area or increase
number of such branch hoses, so that total air delivery cross sectional area at any section is
larger than 0.15 m
2
; avoid local flattening and short distance right angel sharp turning.
Case III: A user recently installed two FR95 air duct type air conditioners and found poor
heating effect and small air delivery. Measured indoor unit air intake temperature was 21.7℃,
indoor unit air delivery temperature was 34℃, room air delivery port temperature was 28℃,
outdoor ambient was 8.2℃, operating current was 11.5A and heating pressure was 1.4Mpa.
Analysis: (1) Under nominal operating condition, rated operating current was 16A and heating
pressure was 1.8Mpa; amount of freon in the unit was apparently small; (2) There was no
return air port in any room and air return depended on side doors; (3) The static pressure box
had an air delivery hole and was too near indoor unit air return, causing air short circuit and
affecting air delivery in other rooms.
Solution: (1) Add freon to specified value and carry out overall leakage detection of pipeline;
(2) Provide effective air return twice the size of air delivery port area to ensure favorable
energy cycling and no loss; (3) Block static pressure box air delivery hole and provide thermal
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