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									    EQuilibrium TM Housing InSight

Riverdale NetZero Active Solar Thermal System
Riverdale NetZero is a new semi-detached duplex on a prime inner-city site in Edmonton, Alberta. Each two-storey home
is approximately 234 m2 (2,519 sq. ft.), including the basement. As a winning project in the CMHC EQuilibriumTM Sustainable
Housing Demonstration Initiative, the builder–developer, Habitat Studio & Workshop Ltd., has designed and constructed these
homes with the intent that they are healthy and comfortable to live in, reduce energy use to a minimum, produce as much
energy as they require in a year, conserve resources, have low environmental impact, and are marketable. One of the novel
features of the Riverdale NetZero EQuilibriumTM project, which is highlighted in this EQuilibriumTM Housing InSight, is its solar
combi-system where active solar thermal collectors are used for both domestic hot water and space heating.

Technical Specifications
The Riverdale NetZero solar combi-system utilizes liquid-
based active solar thermal collectors that the Riverdale team
estimates will provide 83% of domestic water heating and
21% of the annual space heating needs. Figure 3 shows the
major components used in the heating, domestic hot water,
and ventilation systems. The four main components of the
solar combi-system include:
n   seven, vertically mounted, drainback solar collectors
    covering 21 m2 in area (Figure 1);
n   a 17,000 litre seasonal heat storage water tank;
n   a 300 litre domestic hot water (DHW) storage tank; and
n   a 7 kW (2 ton) water-to-water heat pump.                       Figure 1     South elevation showing the vertical solar
                                                                                thermal collectors
To extract and store solar thermal energy, heated water from
the solar collectors first passes through a heat exchanger         To boost the amount of solar heat that can be drawn from
in the 300 L DHW tank, and then through a second heat              the seasonal storage tank, a 7 kW (2 ton) heat pump was
exchanger in the 17,000 L seasonal heat storage water tank.        added to the system. The heat pump is able to access an
In addition to the solar thermal energy, two back-up heat          additional 2 GJ (500 kWh) of heat in the seasonal storage
sources were added to the design. The first is the electric        tank by drawing the water temperature down from 30°C to
heating element in the DHW tank. If the water in the               5°C. The resulting lower tank temperature also allows for
seasonal storage tank is not sufficiently hot for space            more solar thermal energy to be captured by the system due
heating, hot water will be circulated from the DHW tank            to the larger temperature difference between the tank and
to the fan coil unit.                                              the solar collector.
         Riverdale NetZero Active Solar Thermal System

         DHW is drawn from the 300 L DHW tank, which is
         maintained at a minimum temperature of 55°C by an
         electric heating element in the tank. The water that
         replenishes the DHW tank is drawn from the municipal
         water mains, and then is preheated by first going through
         a drain water heat recovery unit and then through a heat
         exchanger in the seasonal storage tank before entering the
         bottom of the DHW tank.
         The space heating system is a forced air system with heat
         supplied through a hot water coil in the fan coil unit.
         The heated water used in the fan coil unit can be drawn
         from a number of sources depending on the availability
         of water of sufficient temperature:
         1. from the seasonal heat storage tank to the fan coil;
         2. from the seasonal heat storage tank through the heat
            pump to the fan coil; or
         3. from the DHW tank to the fan coil.
         Flat plate solar collectors were selected for this system,
         which have the following specifications:                       Figure 2    Utility Room Solar Plumbing Layout

         n   Collectors are 1.776 m tall, 1.751 m wide,
             and 0.105 m deep;                                          Implementation Considerations
         n   A solar aperture area of 2.75 m ;2
                                                                        The schematic in Figure 3 of the solar combi-system shows
         n   A weight of 55 kg; and                                     the complexity of the system, which in turn brought
         n   A minimum life expectancy of 25 to 30 years.               challenges into various aspects of the project. Although
                                                                        the system was designed to maximize the amount of
         The collectors were designed to be used as part of a
                                                                        energy drawn from the solar and heat recovery systems,
         drainback system. A drainback system utilizes gravity
                                                                        the Riverdale NetZero team concluded that the system was
         to drain the fluid from the collectors to a 30-litre storage
                                                                        somewhat difficult to design and install, complicated to
         tank whenever the water in the collectors is cooler than
                                                                        model and estimate performance, and complex to document
         the seasonal heat storage tank. This allows water to be
                                                                        and explain.
         used as the collector fluid without the risk of freezing,
         even in winter. The drainback tank needs to be installed       Figure 2 shows the solar plumbing layout in the utility
         lower than the collectors in order to operate.                 room. Though the plumbing looks complex to describe, it
                                                                        can be simplified by explaining it as sections of heat-flow
         The 17,000 litre seasonal storage water tank was built
                                                                        loops that provide various heating functions: solar heat
         on site out of poured in place concrete. The tops and walls
                                                                        collection, domestic water heating, heat transfer between
         of the tank have RSI-8.8 (R-50) insulation, and the bottom
                                                                        tanks, flexible operating configurations, and ground loop
         has RSI-3.5 (R-20) insulation.
                                                                        cooling. Once commissioned, the piping will be insulated,
                                                                        and the pipes will be colour coded with directional arrows.

2   Canada Mortgage and Housing Corporation
                                                            Riverdale NetZero Active Solar Thermal System

When mounting solar devices for DW heating, it is often          n   Plumbing codes that do not address such systems
recommended to install the collectors at an angle close to           and the lack of familiarity of inspectors with solar
the latitude of the site. While, the latitude in Edmonton is         combi-systems.
53°N, the team opted for a vertical (90°) installation for the
solar thermal collectors to maximise the winter solar heat
                                                                 Cost Implications
production. Benefits of the vertical installation for solar      The Riverdale NetZero team reported that the cost of
thermal space heating systems include:                           the solar thermal system was approximately $37,000.
                                                                 They estimated that the system will supply approximately
n   Good winter solar gains;
                                                                 4,150 kWh per year of solar energy to the house per year.
n   Elimination of snow accumulation on the panels which         When the costs are spread over 25 years, the cost of solar
    can reduce the amount of solar energy absorbed;
                                                                 energy supplied by the system is $0.35/kWh. However, by
n   Maximisation of the capture of reflected solar energy        discounting the $410/year fixed natural gas connection fee
    from snow covered ground;                                    that is saved by using only solar energy and electricity to
n   Minimisation of overheating in the summer; and               heat the home and domestic hot water, the 25-year price
n   More roof space for the photovoltaic (PV) system.            of the active solar heat drops to $0.25/kWh.
Given the weight and size of the collectors, a crane was used    To the surprise of the team, without including the elimination
to install the collectors.                                       of the gas connection fee, the cost of energy produced from
Another challenge in implementing the system was that the        the solar thermal system was found to be greater than the
interior space required for the tanks, pumps, and piping was     25-year price of electricity generated from the PV system.
considerable as was the amount of wall space required for        The 5.6 kW PV system, which generates approximately
the system plumbing.                                             6,600 kWh of electricity per year, was reported to cost
                                                                 $54,000. Over 25 years, this represents a solar energy cost
Installation problems encountered by the team when               of $0.33/kWh. Note that neither of the energy price estimates
commissioning the system included:                               includes maintenance or financing costs.
n   Air locks in piping and cavitation in the pumps;             At first glance, it might not be evident why the solar
n   Leaks in valves, piping joints, pumps; and                   electrical energy would be less expensive than the solar
n   High level of complexity in developing settings and          thermal energy: PV modules cost between $500 to
    algorithms for the control system to maximise                $1,100 per square metre with efficiencies ranging from
    performance.                                                 13% to 17%, while flat-plate solar thermal collectors cost
Other challenges faced by the team in implementing their         $300 to $400 per square meter with efficiencies ranging
solar combi-system included:                                     from 30% to 60%.
n   A lack of design tools for solar thermal systems for both    For solar thermal systems with one or two collectors
    domestic hot water and space heating;                        supplying a solar DHW system, the energy price for
n   A lack of trades with basic training on solar thermal        solar thermal heat would be much less than solar PV
    installation; and                                            energy. However, beyond 1 or 2 collectors, the systems
                                                                 provide diminishing returns due to extended periods
                                                                 when the system is oversized and thus the solar resource is
                                                                 underutilized. The first collector meets most of the domestic
                                                                 hot water needs in the summer, whereas the energy provided
                                                                 from additional collectors is generally only utilized in
                                                                 winter and in the shoulder seasons. Thus every additional

                                                                                              Canada Mortgage and Housing Corporation   3
         Riverdale NetZero Active Solar Thermal System

         collector provides a smaller amount of usable energy for       Summary
         roughly the same cost per collector. In comparison, none
                                                                        Harnessing solar energy is a key element utilized by all
         of these challenges are a factor for grid-connected solar PV
                                                                        EQuilibrium teams to approach and achieve net-zero annual
         systems, whose efficiencies are not dependent on the home’s
                                                                        energy consumption. Active solar systems can supply heat
         electricity demand.
                                                                        for both space heating and domestic hot water, as well as
         Technology Benefits                                            electricity. The Riverdale NetZero team found that given
                                                                        the mismatch between when peak space heating demands
         Energy Savings                                                 occur compared to peak solar availability, a number of
                                                                        design strategies need to be applied in order to maximise the
         The Riverdale NetZero team estimates that the solar thermal
                                                                        fraction of space heating demands that can be met with solar
         system is expected to produce:
                                                                        energy. Some of these strategies can add complexity and
         n   1910 kWh/year of usable energy for DHW heating; and        cost to the system that make implementing the solar space
         n   2240 kWh/year of usable energy for space heating.          heating system more challenging then solar electric systems
         The sun’s renewable energy will thus provide 83% of the        that do not face the same challenges.
         domestic water heating and 21% of the space heating needs.

4   Canada Mortgage and Housing Corporation
                                                    Riverdale NetZero Active Solar Thermal System

Figure 3   Schematic of Major Components of Riverdale NetZero Liquid-Based Active Solar Thermal System

                                                                                   Canada Mortgage and Housing Corporation   5
        Project Team
        Primary contact: Gordon Howell
        Howell-Mayhew Engineering
        Builder–developer: Habitat Studio & Workshop Ltd.
        Builder contact: Peter Amerongen

        For more information about this project and
        other EQuilibriumTM housing projects, visit
        CMHC’s website at

           What is EQuilibriumTM Housing?
           The national EQuilibriumTM Sustainable Housing Demonstration Initiative, led by Canada Mortgage and Housing Corporation
           (CMHC) brings the private and public sectors together to develop homes that address occupant health and comfort, energy
           efficiency, renewable energy production, resource conservation, reduced environmental impact and affordability.
           CMHC’s EQuilibriumTM housing initiative offers builders and developers across the country a powerful new approach to
           establish a reputation for building affordable, premium quality healthy homes that will meet the needs of Canadians now
           and well into the future.
           EQuilibriumTM housing combines a wide range of technologies, strategies, products and techniques designed to reduce a
           home’s environmental impact to an absolute minimum. At the same time, EQuilibriumTM housing also features commercially
           available, on-site renewable energy systems to provide clean energy to help reduce annual energy consumption and costs.

           EQuilibriumTM Housing InSight
           EQuilibriumTM Housing InSight present specific housing design strategies and technologies implemented in EQuilibriumTM
           housing demonstration projects.

           CMHC has been Canada’s national housing agency for more than 60 years. CMHC is committed to helping Canadians
           access a wide choice of quality, affordable homes and making vibrant and sustainable communities and cities a reality across
           the country. To find out more about how the Government of Canada and CMHC are working to build stronger homes and
           communities for all Canadians, call CMHC at 1-800-668-2642 or visit

                                                                                                          ©2009, Canada Mortgage and Housing Corporation
                                                                                                          Printed in Canada
                                                                                                          Produced by CMHC             12-08-10

          This publication is intended to highlight housing technologies and practices the builder teams utilized to construct their projects
          under CMHC’s EQuilibriumTM Sustainable Housing Demonstration Initiative. It is provided for general information purposes only
          and does not constitute an assessment, recommendation or an endorsement of any system, strategy, technique, technology, or product;.
          The predictions for building performance contained in the publication have been provided by the individual builder teams based on
          computer modeling and current understandings of best construction practices. Actual building performance may vary. Reliance on
          the information in this publication for the purpose of planning, design or construction activities would not be appropriate. If readers
          intend to engage in activities of that nature, they are advised to consult appropriate professional resources to determine what is safe
          and suitable in their particular case. Any reliance or action taken contrary to this advice is the full responsibility of the user. Canada
          Mortgage and Housing Corporation assumes no responsibility for any consequence, expense, claim, damage or loss arising from the

          use of the information contained in this publication.

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