Overview
This is an ideal model of an air handling unit (AHU), primarily to
calculate the thermal energy consumption of an air handling unit
(AHU) but also the electric power. The model is mainly based on
thermodynamic equations.
It is based on incoming and outgoing enthalpy flows of moist air
(thermodynamic principle).
The model aims to need
little computational effort. Therefore state machines represent the
basis of the model and no Modelica Fluid is used.
If simulation runs instable, reduce clockPeriodGeneric and/or use one
of the alternative equations for the calculation of
p_sat_surface in both dehumidification state machines
(see source code of these state machines).
Assumptions
For further explanation for each parameter see noted sources and [1]!
Please note that the assumptions are made regarding AHUs which are
implemented in laboratories.
- BPF_DeHu: by-pass factor of cooling coil during dehumidification;
Expression for the amount of air that by-passes unaffectedly over a
coil while the remaining fluid comes in direct contact with the coil.
[2, p. 500]; BPF_DeHu between 10 % and 35 % acc. to [3]
- efficiencyHRS_enabled: temperature differential; efficiency of
heat recovery system (HRS) when it is enabled (for HRSs without
sorptive technology efficiencyHRS_enabled = 0.6 ... 0.8 [4])
- efficiencyHRS_disabled: temperature differential; efficiency of
heat recovery system (HRS) when it is disabled (proposal for
parameter efficiencyHRS_disabled = 0.2 ... 0.4 [1])
- dp_sup, dp_eta: pressure drop over ventilator; recommendation dp
= 800 Pa [7]
- eta_sup, eta_eta: efficiency of supply/extract air fan. Assumed
as constant in this model.
Known Limitations
- static model, not dynamic
- no technical restrictions (demanded goal/value will always be
reached)
- no implementation of merging two or more mass flows
- only adiabatic humidification
- no moisture transfer in HRS
- the pinch temperature HRS component is 0 K
- if absolute humidity of outside air (input connector
"X_outdoorAir) exceeds X_saturated(T_oda) calculated with phi=1,
X_oda is set to X_saturated
Concept
- Producing output data (thermal and electric power and outgoing
air flow rate) by using some input data (black-box-principle). The
inner components of an AHU are considered within this model.
- Based on sketch/schema of AHU shown in figure 1 [5, appendix D].
- This model of an AHU is able to represent 5 cases: only heating,
only cooling, dehumidification, humidification plus heating,
humidification plus cooling.
Figure 1 [5, appendix D]
References
- [1] Mehrfeld, P. (2014): Experimentelle Untersuchung von
Lüftungstechnik in Laboren (master thesis). RWTH Aachen University,
Aachen. E.ON Energy Research Center, Institute for Energy Efficient
Buildings and Indoor Climate; supervised by: Lauster, M.; Müller, D.
- [2] Khurmi, R. S.; Gupta, J. K. (2009): Textbook of Refrigeration
and Air Conditioning. 4th ed. New Delhi: Eurasia. (682 pages). ISBN
9788121927819.
- [3] Lindeburg, M. R. (2013): Mechanical Engineering Reference
Manual for the PE Exam. 13th ed. Belmont: Professional Publications,
Inc. (1488 pages). ISBN 9781591264149.
- [4] Verein Deutscher Ingenieure e. V.: VDI 2071:1997-12:
Wärmerückgewinnung in Raumlufttechnischen Anlagen. Richtlinie.
Berlin: Beuth Verlag GmbH.
- [5] Deutsches Institut für Normung e. V.: DIN V 18599-3:2011-12:
Energetische Bewertung von Gebäuden – Berechnung des Nutz-, End- und
Primärenergiebedarfs für Heizung, Kühlung, Lüftung, Trinkwarmwasser
und Beleuchtung – Teil 3: Nutzenergiebedarf für die energetische
Luftaufbereitung. Vornorm. Berlin: Beuth Verlag GmbH.
- [6] Schweizerischer Ingenieur- und Architektenverein (2006): SIA
2024: Standard- Nutzungsbedingungen für die Energie- und
Gebäudetechnik. Merkblatt.
- [7] Gilroy, E.: Designing - Building Services: fan power, it will
blow you away! PM Group. Online available at
http://www.pmgroup-global.com/pmgroup/media/News-Attachments/
Fan-Power,-it-will-blow-you-away!pdf, last accessed on 23 September
2014.
Example Results
20 validation experiments are documented in [1, chapter 4 and 5].
-
February, 2016 by Philipp Mehrfeld:
Added previous() functions in source code as decisions for state
machines and calculations in state machines did not use values of
the same time step.
-
June 17, 2015 by Philipp Mehrfeld:
Changes in Inputs, transition conditions, BPF_DeHu, etc. Added
functionality for mode selection.
-
Septmeber, 2014 by Philipp Mehrfeld:
Model implemented
Contents
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.AixLib.Airflow.AirHandlingUnit.AHU
