ECONET ®Manual for calculation of
temperature efficiency
January 2008
How are the temperatures obtained?
The temperatures GT00, GT10 and GT20 on the air side are
obtained from the unit's automatic control system or from
the ECONET automatic control system (available as an
accessory).
The temperatures GT40, GT41 and GT42 on the liquid
side can be obtained from the ECONET regulator via
LON/Modbus or as 0-10V signals.
Where is the temperature efficiency
calculated?
Alternative 1:
The temperature efficiency is calculated in the unit's auto-
matic control system. The necessary liquid temperatures
can be obtained from the ECONET regulator, either as 0-
10 V signals or via network communication.
Alternative 2:
The temperature efficiency is calculated in the ECONET
automatic control system and can be obtained as a 0-10 V
signal from the ECONET regulator. This is a supplemen-
tary function and must be selected in conjunction with the
dimensioning of the unit (accessory). In this case, Fläkt
Woods supplies 4 temperature sensors (GT00, GT10,
GT21 and GT22) for installation on the air side. The
sensors must be installed on site (not included in the Fläkt
Woods delivery). Exhaust air flow sensors are also
supplied, because an efficiency without knowledge of the
air flows is relatively meaningless.
Both alternatives 1 and 2 are possible, although alterna-
tive 1 will make follow-up and logging easier. Depending
on the design of the BMS system, it may even be possible
to monitor the function of the unit via the Internet.
Other
When considering a measured temperature efficiency, it is
important to be able to analyse/evaluate the obtained
result. The tolerances for the sensors that are used in a
ventilation context are relatively high, e.g. air flow,
temperature sensor, etc., which in turn leads to an inaccu-
racy in the temperature efficiencies.
NOTE: It is recommended that the obtained result is
used as an indicator, and not as a scientific result.
Factors which influence the result:
– Balance of air flows (supply air/exhaust air
proportion)
– Sensor tolerance, can give a deviation of approxi-
mately 10% in the efficiency
– Positioning of sensors, e.g. the temperatures on the
air side must be correctly positioned and must be
representative.
– Energy quantity in the exhaust air (flow, tempera-
ture, enthalpy)
– Type of frost protection fluid.
ECONET®
Manual for calculation of temperature efficiency
Fläkt Woods 8420 GB 2008.01 2 Subject to alteration
ECONET®MANUAL
Temperature efficiency
The standard definition of temperature efficiency in an air
handling unit is a supply air temperature efficiency that is
calculated over the recovery coil for the supply air.
The supply air temperature efficiency is calculated as:
η= (GT10-GT00)
(GT20-GT00)
where:
GT00 = outdoor temperature before of the supply air coil
GT10 = supply air temperature after the supply air coil
GT20 = exhaust air temperature ahead of the exhaust
air coil
Because external energy is supplied to the recovery circuit
in an ECONET system, it is not possible to calculate a
supply air temperature efficiency according to the tradi-
tional formula.
In order to obtain a comparable value, the supplied
energy should be excluded from the calculation model.
The following formula can be used for this purpose, i.e.
the liquid temperatures in the circuit can be used to
remove the effect of the supplied energy on the supply air
temperature efficiency.
η= (GT42-GT41) x (GT10-GT00)
(GT40-GT41) x (GT20-GT00)
where:
GT40 = liquid temperature before of the supply air coil
GT41 = liquid temperature after the supply air coil
GT42 = liquid temperature after the exhaust air coil
If no external energy is supplied to the ECONET circuit,
the traditional calculation model can also be used.
If it is wished to calculate temperature efficiencies in the
summer (cooling recovery), it would be most appropriate
to use an exhaust air temperature efficiency. This is
because condensation can occur on the supply air coil, at
least in ECONET systems, in which case the supply air
temperature efficiency will be misleading.
The exhaust air temperature efficiency is calculated as
follows:
η= (GT21-GT20)
(GT00-GT20)
where:
GT00 = outdoor temperature ahead of the supply air coil
GT20 = exhaust air temperature ahead of the exhaust
air coil
GT21 = extract air temperature after the exhaust air coil
When analysing the efficiency of a recovery unit, it is
extremely important to gather as much data as possible
from the system. For ECONET, it is recommended to enter
the details included at the end of this document.
To be able to make an analysis, as much data as possible
should be obtained from the project.
Input data
Temperatures
GT00: ºC, outdoor temperature
GT10: ºC, supply air temperature
GT20: ºC, exhaust air temperature
GT21: ºC, extract air temperature
GT40: ºC, fluid in supply air coil
GT41: ºC, fluid out supply air coil
GT42: ºC, fluid out exhaust air coil
Flow
GF10: m³/s, supply air flow
GF20: m³/s, exhaust air flow
GP41: l/s, liquid flow
Other
HRC: V, heat recovery signal
FO10: Hz, frequency supply air fan
FO20: Hz, frequency, exhaust air fan
FO40: Hz, frequency, pump
SV40: %, position of shunt valve
ECONET®
Manual for calculation of temperature efficiency
Fläkt Woods 8420 GB 2008.01 3 Subject to alteration
ECONET®MANUAL
Fläkt Woods Group Brings Air to Life
Fläkt Woods Group provides a full range of products and solutions for
building ventilation, air treatment and industrial air movement.
FWG-Econet-Manual-GB-2008.01-8420 Condesign Infocom AB +46 36 30 83 80
Sales Offices available worldwide – See our website for details.
www.flaktwoods.com
Head offices
Buildings Air Climate
Fläkt Woods AB
Kung Hans väg 12
SE-192 68 SOLLENTUNA
Sweden
t+46 771 26 26 26
f+46 8 626 73 10
Industry Air Movement
Fläkt Woods Limited
Tufnell Way
COLCHESTER, CO4 5AR
United Kingdom
t+(0) 1206 544122
f+(0) 1206 574434
Due to a policy of continuous development and improvement the right
is reserved to supply products which may differ from those illustrated
and described in this publication. Certified dimensions will be
supplied on request on receipt of order.
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