CanSIA 2012-Integrating Solar Thermal with Geothermal

Thanks to the Photovoltaic Innovation Network, I participated in Solar Canada 2012 in Toronto, Ontario. This conference/exhibition is the largest national solar event in Canada, and is hosted by the Canadian Solar Industry Association (CanSIA). This year the event was quite large, in part due to the fact that it was CanSIA’s 20^th anniversary.

In this conference, I participated in some talks and visited some booths; one of the talks that was really interesting to me was about Solar thermal, Geo-thermal and the opportunity to integrate these two technologies together. Solar thermal installations consist of a solar thermal collector on the roof, a control unit with a pump and a potable water storage tank. The collector absorbs the light from the sun and converts it into heat. This heat is transferred to a liquid which circulates through the collector and down into the solar storage tank (fig-1). There are a lot of solar thermal projects within Canada (as they can easily deployed, even in residential areas), but one of the biggest is at Oxford Gardens retirement home in Woodstock, Ontario. This solar thermal project is saving on air conditioning costs by up to 40%, or approximately $20,000 per year; for heat savings, up to 60% or approximately $40,000 per year, according to Suni Ball from Proterra Solar[1].

 

    A geothermal heat pump, ground source heat pump (GSHP), or ground heat pump is a central heating and/or cooling system that pumps heat to or from the ground. It uses the earth as a heat source (in the winter) or a heat sink (in the summer). Heat pumps provide winter heating by extracting heat from a source and transferring it into a building. In the summer, the process can be reversed so the heat pump extracts heat from the building and transfers it to the ground. Transferring heat to a cooler space takes less energy, so the cooling efficiency of the heat pump gains benefits from the lower ground temperature (fig-2).

 

The combination of these two systems has many benefits [2]:

-Both systems don’t use fossil fuels at the point of use

-Geothermal is the backup for the solar thermal while the Geo-thermal can also provide cooling.

-Large flexibility in the heating appliances that can be used with both systems.

-Using the geothermal loop field as a storage tank to absorb the excess solar energy in the summer.  This advantage allows you to oversize the solar thermal system and increase the solar thermal contribution to the winter heating.

A study has been done [3] for the viability of a combined system in Milton, Ontario. This study shows that a combined system is feasible for space conditioning. For the house in this study, the seasonal solar thermal energy storage in the ground was sufficient to offset the large amount of Geo-thermal pump system length that would have been required in conventional systems. They showed that the economic benefit of such system depends on climate, as well as borehole drilling cost.

To conclude, a hybrid Solar-Geo-thermal system could be an outstanding solution to the high demand of energy in today’s world. It has a lot of benefits like sustainability, being clean (non-polluting) and having the ability to work all year round. Another important benefit is the possibility of using this system for all kinds of applications such as residential, commercial and industrial.

-Farbod Ghods

Ph.D Candidate, 1st Year

Department of Engineering Physics

McMaster University

References

[1]-
http://oxfordgardenssolarproject.com

[2]-
http://www.dma-eng.com/

[3]- Rad et al, COMBINED SOLAR THERMAL AND GROUND SOURCE HEAT PUMP SYSTEM, Eleventh International IBPSA conference, Glasgow, Scotland, July 2009.

That’s the power of a vacuum

Humanity is consuming more and more energy every year and, since much of the world depends on fossil fuel based resources, our total carbon emissions continue to climb as well. In the effort to curb this trend, energy conservation is imperative. One area where conservation efforts can make a particularly large impact is in our nation’s buildings where 40% of our national energy expenditure is consumed. [1] This is a powerful motivation to construct buildings that are more energy efficient. Researchers from the National Research Council (NRC) are attempting to do just that with a promising new technology called the vacuum insulated panel (VIP).

It is important to digress somewhat here.  What does it mean to make a building more energy efficient? Well, we have to actively heat and cool our buildings. In other words, we continually supply energy so as to maintain a constant temperature. If we need to supply it constantly then that means we must be losing it somewhere.  The energy expended to heat or cool a structure is lost through the walls, windows, floor, roof, etc. An “energy efficient” building would lose less.

This is what insulation does. It helps to maintain the difference between the interior and exterior temperature by slowing the rate of heat transfer between them thus requiring less energy to heat and cool the structure. The best insulation possible is a vacuum. This is because heat needs some medium through which to travel and a vacuum is essentially the absence of a medium. Everyone knows that a thermos can keep liquids hot for a long time and this is the reason why. It is insulated with a vacuum (in actuality it would not be a perfect vacuum).

This is the same idea behind VIPs. They are constructed from an open nano-porous material that is strong enough to remain intact under atmospheric pressure. The air is evacuated from the panel and then the whole thing is sealed in a gas barrier to prevent any air infiltration. It is essentially a portable, rigid container that holds a vacuum. In terms of performance it blows the competitors away.

Cross-section of a VIP: The core is made from a porous material. (Picture from ref.)

The ability of a material to prevent heat loss is given by its R-value per unit thickness. Familiar insulation materials like mineral fibre or cellulose are less than R-5 per inch. VIPs can achieve R-values as high as R-60 per inch. This is incredibly high and anyone in the building industry would be very skeptical of such a number. However, that’s just the power of a vacuum.

So why haven’t we seen the widespread proliferation of this wonder-material? There are several reasons. Cost is the most prohibitive factor. VIPs are currently more expensive than the alternatives. However, the researchers at the NRC claim that once economies of scale kick in the cost will come down considerably. Another major issue is  uncertainty in the long-term performance of VIPs. The research has yet to establish how this technology degrades over time. They are certainly less robust than convention materials, as a single pinhole in the gas barrier will compromise the vacuum.  Nevertheless, it is a very promising technology and perhaps not too far away from more widespread adoption.

For the NRC paper on VIPs  see:

Mukhopadhyaya P., M.K. Kumaran, F. Ping and N. Normandin. Use of vacuum insulation panel in building envelope construction: advantages and challenges. May 2011. NRC-53942.

http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc53942.pdf

-Erik Janssen

(Engineering Physics, MASc, Year 2 at McMaster University)

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[1] Mukhopadhyaya et al.