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Technical Support > Articles
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Triple-7 sets out pattern for the future |
Published in ACR Today Magazine, March 2003
LORDAN, developers and manufacturers of finned coil heat exchangers,
have introduced the Tripple-7, an advanced coil pattern which
it's claimed provides a higher capacity than any other on the
market.
The Triple-7 coil pattern has 7-mm tubes, the smallest possible
tube diameter for finned coils, equilateral tube arrangement
and the optimal ratio between the tube diameter and tube distance.
Towards small diameter tubes: finned coils appeared with
the introduction of the first air conditioners.
Since then the capacity of finned coils has been improved by
manufacturing the coils with smaller diameter tubes.
Coil capacity increase as tube diameter decreases. Decreased
tube diameter, combined with reduced distances between the tubes,
results in more tubes per fin cross section. The increase in
the number of tubes provides greater primary surface and the
reduced distances between tubes leads to higher fin efficiency.
These properties are responsible for the higher capacity of
small diameter tubes. Capacity is calculated for evaporators
with 0.05m2 face area and same depth, operated with a high performance
fan. The calculation assumes louvered fins and rifled tubes.
Condensers and heater coils yield the same results.
Lordan marketing manager Jano Tyroler said : "It is interesting
to note that the first three coil patterns are still largely
used in the market, despite the advantages offered by small
diameter tube coils."
He explained that some in the industry believe that large coils
should be produced with large diameter tubes and likewise small
diameter tubes are only suitable for small coils.
"This belief stems from concerns relating to excessive refrigerant
or water pressure drop in large coils with small diameter tubes.
However, pressure drops can be reduced by applying more flow
circuits" says Tyroler.
Lordan produces high performance 2.5 m long condensers, evaporators
and heaters using its proprietary Triple-7 coil pattern.
Improved capacity by better air pressures control: the
first 7-mm tube coil with a tube pitch of 25 x 12.5 mm was introduced
about ten years ado and was followed by the introduction of
a 21 x 12.5 mm tube. These two tube pitches are the most common
among the few 7-mm tube coil patterns available today. The triple-7
coil pattern provides a significant capacity improvement compared
to other 7-mm patterns. "Its unique design stems from better
understanding of the variables affecting air pressure drops"
says Tyroler.
"Resistance to airflow in a coil is proportional to the number
of rows deep. In effect, the Triple-7 coil, with fours rows
deep, has a 20 per cent lower air pressure drop compared to
five rows deep coil".
In addition, resistance to airflow depends on the amount of
space between two adjacent tubes. The Triple-7 has the largest
gap between two adjacent tubes resulting in the lowest resistance
to airflows.
"With the Triple-7 coil, lower resistance to air flow allows
higher air velocity using the same fan" he adds. In other words,
the three 7-mm tube coils have the same fin area and nearly
the same tube area but the Triple-7 provides increased performance
due to higher airflow.
The Triple-7 coil's increased capacity also results from
the enragement of the tubes in an equilateral pitch.
For the same number of tubes in a given fin size, the equilateral
pitch produces the highest fin efficiency. Simply put: the heat
travels the shortest possible distance from the fins to the
tubes. The Triple-7 coil provided higher capacity and occupies
less volume than any other coil. "With its light weight and
reduced refrigerant requirements, it represents a substantial
saving both in space and cost" concludes Tyroler.
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