HEX Thermal efficiency

File: HEX Efficiency.doc

Last edition: 2003-03-04

Author: Mikael Krantz

History: 96-02-14/MK First released version.

96-09-30/MK Updated to Menta 1.20
Alarm block has new name and text.
Pri added on alarms.

97-08-27/MK Updated to Menta 3.0
Comment in formula corrected.
New FBD layout.

98-12-21/MK New filename

2003-03-04/MK Updated to Menta 4.0

Description

Efficiency calculation with a sensor , here named "Hex temperature" placed;

0 = in the return air, directly after the heat recovery.

1 = in the supply air, directly after the heat recovery.

The formula used for efficiency calculation is depending on where the HEX temperature sensor is placed, in the supply duct, after the HEX, or in the return duct, after the HEX.

Sensor placed;

in return duct in supply duct

t3 - t4 t2 - t1

Formula: ------- -------

t3 - t1 t3 - t1

where t1 = Supply temperature before HEX.
t2 = Supply temperature after HEX
t3 = Return temperature before HEX
t4 = Return temperature after HEX

Efficiency calculation for Heat exchanger with use of an extra air temperature sensor placed after the heat exchanger, in the supply, or in the return duct. The efficiency is calculated as a value between 0 and 100%. An alarm is set if the efficiency is to low while the HEX control is above a set limit. If the numerator or the denominator are below 2°C, or if the running signal is false, the calculation output is zero, and the alarm interlocked.

Inputs

(Real) HEX temperature, °C.

(Real) Outlet temperature before HEX, °C.

(Real) Outdoor temperature, °C

(Real) HEX Control signal, 0-100%.

(Binary) Running signal

Outputs

(Real) Thermal efficiency 0-100%

(Binary) Low alarm thermal efficiency

Parameters

(Real) EfficiencyLimit 40%

(Real) HEXControlLimit 90%

(Binary) EfficReturnSupply

Public signals

(Real) EfficiencyLimit

(Real) HEXEfficiency

(Real) HEXControlLimit

(Binary) HEXAlarm

(Binary) EfficReturnSupply

---