Ryerson University

Project Description

Potential energy savings in residential buildings with better designed HVAC systems

Project Abstract

As concerns for a limited energy future continues to grow, decreasing energy requirements is of
utmost importance. Energy consumption for building environments in developed countries represents a
major part of the total energy consumption (Lee et al., 2006). The residential sector in Canada
contributes to approximately 16% of the total required energy in Canada (Natural Resources Canada
[NRCan], 2006), and it was estimated that heating ventilating and air conditioning (HVAC) system
consumes approximately 60% of the total energy used in residential houses in Canada (NRCan, 2006).
While this significant amount of energy has been used in residential houses to provide thermal comfort
to occupants, studies have found that significant energy savings can be realized by proper sizing and
operating HVAC systems. A lot of efforts have been made in the past century in increasing the energy
efficiency of HVAC systems; however, a huge potential of efficiency improvement still persists. Huang et
al. (2005) shows that a total energy saving of 17% can be achieved with HVAC systems operating with
combining five energy management control (EMC) functions. The five EMCs incorporated in Huang et
al.�s study include outside air economizer, programmed start and stop lead time, load reset and
occupied time adaptive control strategy. As well, an investigation through surveys, simulations, and
experimental studies was carried out in studying the performances of water heating systems in the
United Kingdom and results have shown that improving the control of the heating systems can save up
to 20% of the energy consumption (Liao, 2003). Also, according to a study performed by American
Society of Heating, Refrigerating and Air?Conditioning Engineers (ASHRAE), there exists a significant
amount of potential energy savings in HVAC systems in residential houses in the United States.
Residential houses with high?efficiency equipment save from 24% to 29% on average of the total heating
and cooling costs versus houses equipped with conventional HVAC systems (Lucas et al., 2007).
The energy consumption of HVAC systems in buildings is not solely dependent on the
performances of the HVAC system itself, but also on two other factors, which are the heating and
cooling load of the house, and the occupant�s living habits and behaviour (Peeters et al., 2008). Previous
studies in Canadian houses have mostly neglected the interaction between the occupants� behaviour to
the overall energy load of a residential house and this study aims to fill that gap. This study would
estimate potential energy savings in residential houses and Toronto, Ontario will be used as the
reference city.
Scope of Study
The heating and cooling load of the house is usually overestimated in Canadian houses because
most HVAC systems in residential houses in Canada utilize a single zone HVAC system for conditioning
air throughout the entire house. The use of single zone systems led to inefficient heating or cooling due
to the differences in thermal load in the different spaces of the house (Wang & Jin, 1999; Refern et al.,
2007). This in turn reduces the thermal comfort of occupants as well as consumes a lot more energy for
over?conditioned spaces. As an alternative, multiple zone systems were suggested. Multiple zone
systems could effectively mitigate the problem by separating the house into different conditioning zones.
Multiple thermostats with its associated set points can be established to accommodate to user?specific
living habits. However, it has not been widely adopted due to its high capital costs and extensive spaces
needed (Refern et al., 2007). To mitigate the two drawbacks of typical multiple zone systems, the recent
development of inferential sensors have enabled a more cost?effective multiple zone system to be
Heating and cooling load is also significantly affected by the configuration of building envelope
systems. Building envelope is the boundary that separates the interior conditioned space to the exterior.
To reduce the heating and cooling load of the house, materials with higher insulation value is usually
incorporated into the envelope system to minimize the heat loss or gain through the envelope.
Windows are typically the major source of heat loss through the envelope system due to its high heat
transmittance value. During heating season, which is approximately 60% of the year in Toronto
(Richman & Pressnail, 2008), North facing windows losses a much more significant of heat than east,
west, and south facing windows (Schoenau, 1983).General design procedure is to install highly insulated
windows in the north?facing wall to reduce heat loss and install windows with high solar heat gain
coefficient in the south to maximize passive solar heating (Persson et al., 2005). The original purpose in
incorporating fenestrations within a house is for establishing a visual connection between the occupants
and outdoor. However, not all occupants make use of this original purpose and the rare frequency
might not be justified with the amount of heat loss through these glass structures throughout the year.
This observation has to be investigated on further to quantify and to better understand today�s situation.
As well, it is believed that when occupants are feeling abnormally warm or cold, they would
prefer opening the windows in allowing natural ventilation to cool or heat the spaces. This would lead to
a substantial amount of conditioned air being evacuated to the outdoor and therefore energy used in
conditioned the air is therefore wasted. Proper protocol in dealing with overheated or cooled spaces is
to configure the thermostat settings to better reflect the occupants� need and thermal comfort. The
tendency of occupants improperly opening the windows is also subjected to further research to
establish a better understanding on this observation.
To estimate potential energy savings in residential houses, today�s situation has to be
investigated first. A combination of theoretical analysis and literature review will take place through a
series of library research. An on?site survey will be conducted on residential home tenants about their
living habits and general feeling towards existing envelope and HVAC systems installed at their houses.
Critical information will be gathered and studied on. Factual question such as the amount spent on
electricity and natural gas monthly, the number of windows installed in their house, and the type of
HVAC system installed etc. will be enquired to evaluate the performances of their existing system and
the heating and cooling load of the house. A benchmark home will be established for energy modeling in
later stage of the study.
In the second part of the study, an energy modelling will be conducted to quantify the potential
energy savings in Toronto houses by simulating conventional control techniques and more advanced
control strategies, such as inferential control schemes in the benchmark home. Based on the results of
these simulations, short term (i.e. daily or weekly) and long term (i.e. seasonal and annual)
performances of the different control schemes can be evaluated and the potential for employing
advanced control techniques could be identified and explored. On?site experimentations will be carried
out in testing and verifying the findings. Work carried out will be in conjunction with a Natural Sciences
and Engineering Research Council of Canada (NSERC) funded project, entitled �inferential sensors and
inferential control scheme for use in building automation� by Dr. Zaiyi Liao.

Surveys released for this project:
Cost and energy savings in heating and cooling sys 62
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