(1) PAPER TITLE

“An Ageing Operator and its Use in the Highly Constrained Topological Optimization 
of HVAC System Design”.

(2) AUTHOR DETAILS

Jonathan Wright,
Department of Civil and Building Engineering,
Loughborough University,
Loughborough,
Leicestershire,
LE11 3TU
UK

Email:	J.A.Wright@lboro.ac.uk
Tel: 	+44 (0)1509 222621

Yi Zhang,
Institute of Energy and Sustainable Development,
Queens Building 1.05,
De Montfort University, 
The Gateway, 
Leicester, 
LE1 9BH
UK

Email:	YIZhang@dmu.ac.uk
Tel: 	+44 (0)116 207 8712

[Note, the work leading to the human competitive result was conducted while Yi 
Zhang was at Loughborough University and therefore the work is not associated in 
anyway with De Montfort University.]

(3) CORRESPONDING AUTHOR

Jonathan Wright

(4) ABSTRACT

“The synthesis of novel heating, ventilating, and air-conditioning (HVAC), system 
configurations is a mixed-integer, non-linear, highly constrained, multi-modal, 
optimization problem, with many of the constraints being subject to time-varying 
boundary conditions on the system operation. It was observed that the highly 
constrained nature of the problem resulted in the dominance of the search by a single 
topology. This paper, introduces an new evolutionary algorithm operator that prevents 
topology dominance by penalizing solutions that have a dominant topology. The 
operator results in a range of dynamic behavior for the rates of growth in topology 
dominance. Similarly, the application of the ageing penalty can result in the 
attenuation of topology dominance, or more severely, the complete removal of a 
topology from the search. It was also observed that following the penalization of a 
dominant topology, the search was dynamically re-seeded with both new and 
previously evaluated topologies. It is concluded that the operator prevents topology 
dominance and increases the exploratory power of the algorithm. The application of 
an evolutionary algorithm with ageing to the synthesis of HVAC system 
configurations resulted in a novel design solution having a 15% lower energy use than 
the best of conventional system designs.”


(5) CONFORMING HUMAN COMPETITIVE CRITRIA

D,E,G.

(6) STATEMENT

Heating, ventilating, and air-conditioning (HVAC) systems maintain the thermal 
comfort of building occupants together with the quality (freshness) of the indoor air. 
Thermal comfort is maintained by controlling the temperature and humidity of the air 
in each zone, and the indoor air quality by supplying sufficient quantities of outdoor 
air to flush each zone of pollutants (a zone consists of a number of rooms, all of which 
have a similar function and experience similar thermal loads). HVAC systems are 
constructed from components that can heat, cool, dehumidify and humidify air, as 
well as mix two air streams. The performance of a system is influenced by the choice 
of components, their topological connection, and the system operation.

Each zone in the building is subject to time varying thermal loads that arise due to 
heat transfer through the building envelope and due to variability in occupancy and 
equipment use. In most commercial buildings, a number of different zones are 
conditioned using a single “multi-zone” HVAC system. Multi-zone HVAC systems 
must be able to maintain the conditions in each zone, even when there is a difference 
in the thermal loads between zones.

The difficulty associated with the design of a multi-zone HVAC system is in 
designing a configuration that can offset both the sensible (temperature) and latent 
(humidity) loads in each zone without compromising the outside air flow rate to each 
zone. This task is made more difficult in that the thermal loads and condition of the 
ambient air entering the HVAC systems vary diurnally and seasonally, and therefore, 
there system must be designed to operate for many boundary conditions. The 
established system configurations are workable in that they can maintain the zone 
temperatures, but many are unable to guarantee control of the zone humidity for all 
boundary conditions, and/or that adequate quantities of outside air will be supplied to 
each zone. Further, all established systems are sub-optimal in their energy use. In 
comparison, the configuration synthesized by the evolutionary algorithm is able to 
maintain the temperature, humidity, and indoor air quality of all zones, at all boundary 
conditions, and is near-optimal in its energy use. The solution conforms to the 
following criteria for a human-competitive result.

(D) The result is publishable in its own right as a new scientific result, independent of 
the fact that the result was mechanically created. 

A paper describing the novel system is in the process of being written and will be 
submitted, together with other papers describing the optimization approach, to the 
“International Journal of Heating, Ventilation, Air-Conditioning and Refrigeration 
Research”.

(E) The result is equal to or better than the most recent human-created solution to a 
long-standing problem for which there has been a succession of increasingly better 
human-created solutions. 

The first “air-conditioner” was developed by Willis Carrier in 1902 to control levels 
of humidity inside a printing company building; Carrier subsequently patented his 
invention in 1906. Systems for air-conditioning single rooms evolved into multi-zone 
air-conditioning systems during the 1960’s. The multi-zone HVAC system 
configurations used in contemporary buildings came to prominence in the 1970’s with 
the two most common configurations being based on the “variable-air-volume” 
(VAV) system and the “dual-duct” system. Since they were first introduced, they have 
been subject to continual improvement, there now being several variants on both 
themes. Both systems continue to be the subject of research and development, 
particularly in relation to their control (for examples, use http://scholar.google.com/ to 
search on “vav hvac” or “dual-duct hvac”). In comparison to these systems, the 
system synthesized by the evolutionary algorithm operates with a lower energy use, 
while providing better control of zone temperature, humidity and indoor air quality. 
The system is therefore considered to be better-than the human-created solutions.

(G) The result solves a problem of indisputable difficulty in its field.

A measure of the accepted difficulty of the problem in the field is that the research 
leading to the result, was conceived, promoted and funded by the American Society of 
Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). The ASHRAE 
Technical Committee responsible for the conception and promotion of the work has 
members who are Professors at prestigious institutions such as the Massachusetts 
Institute of Technology, Purdue University, the University of Illinois at Urbana-
Champaign, together with staff from the US Lawrence Berkeley National Laboratory 
and National Renewable Energy Laboratory. The committee also has members who 
are academics at European Universities as well as representatives from Industry. 

Over a hundred years of research and development has led to multi-zone HVAC 
systems that are able to maintain zone temperature, but without the guarantee that 
zone humidity and indoor air quality will be maintained, These systems also operate 
with a high energy use. The difficulty in conceiving new system configurations is 
evident when it is considered that such systems are required to simultaneously 
maintain the temperature, humidity, and indoor air quality in several different rooms, 
when the pattern of thermal loads between the rooms and condition of the ambient air 
entering the system both vary with the time of day and season. However, the system 
synthesized by the evolutionary algorithm meets these criteria and in effect solves this 
design problem.


(7) CITATION

Wright J A, and Zhang Y, 2005, “An Ageing Operator and its Use in the Highly 
Constrained Topological Optimization of HVAC System Design”, GECCO 2005, 
Washington DC, USA.


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