Hotel Diaries: Geothermal, The Holy Grail of Heating/Cooling

Editor's Note: Continuing with our down-to-earth Hotel Diaries series, Tom Rand, starting with an old shell of a building as raw material, is taking us on a virtual tour of the development process as he works to create a green hotel in Toronto, Canada -- aiming at an 80% carbon reduction over standard buildings, all whilst still thinking like a businessman (i.e. not over-capitalising). Geothermal – the lowest hanging fruit on the carbon-reducing tree, as far as I can tell (1). I’m convinced I’m going to hit at least 40-50% (perhaps more) of my 80% carbon-reducing diet on this technology alone – certainly the lion’s share. What does this entail? Well, down this narrow lane-way (see photo at right), we’re going to get some drill-rigs to drill a bunch of 300 foot holes, put in some pipes, and start exchanging heat and cold with the ground. This week I’ll talk about what geothermal is, from a “how the heck does it work?” perspective. Next week, I’ll talk about the economics and carbon-reduction numbers, and the massive potential geothermal has as a very underused energy source.

None of the other options I looked at (2) compare to geothermal. A geo system is so efficient that for each unit of energy put in, it gets out three to five units of energy! Magic! It gets out five times as much energy as a conventional high-efficiency furnace! Putting geo into a typical home is, from a carbon perspective, equivalent to planting an acre of trees, or taking two cars off the road! What technology can compete with that?! The holy grail of heating and cooling, I say. So – geothermal heating and cooling – what is it? First off, it’s not ‘deep geothermal’ – by that I mean drilling deep down to get at the heat given off by the core of the earth, and using it to make steam, drive a turbine and generate electricity. If you want to know about that technology see here. It’s a great technology in its own right, but it’s not what I’m talking about here. Geothermal heating and cooling, often called geoexchange, involves the exchange (!) of heat (or cold, depending on your thermodynamic perspective on things) with the ground beneath your feet. How deep do you have to go? Well, if you’ve got a yard in which to loop a pipe, only six feet or so .... seriously ... How does it work? Well, let’s do the heat cycle first. You can see a diagram here. The ground stores heat - anything under around six feet deep stays roughly constant at 14°C, year round. There are two tricks to making that heat work for you. First trick: get at the heat and bring it into the house. That’s easy – just install a bunch of pipes and run liquid through it. The pipes will exchange heat with the surrounding dirt (or water, or rock), and the liquid will retain some of the heat, bringing it up into the house. How much pipe do you need? Depends on how much heat you need. A couple of hundred meters, normally. For this hotel? Something like a kilometer of the stuff. Second trick: amplify the temperature difference. That 14 degree liquid needs – somehow - to generate a more comfortable 23 or 24 degree air source. This is more complicated, but something called a heat-pump takes care of all the magic – it’s like a refrigerator running in reverse. The liquid coming out of the ground comes out a few degrees warmer than the liquid going down. The liquid is of a form, and at a pressure, such that the difference in temperature corresponds closely to a phase change. We all know from science class that it takes way more energy to change water from 1 to –1 degree, at standard air pressure, than from 9 to 11 degrees, since the water undergoes a phase change to ice at that point. Well, the glycol – or whatever alternative they use – is at a pressure in the pipes such that it crosses a similar threshold as it heats up (in the ground) and cools down (in the heat pump). That energy is taken from the liquid and exchanged with the air. Still seems pretty weird. Liquid in at 16 degrees, out at 12 degrees and a bunch of hot air is produced at 30 degrees. What?! A good way to think of it is that the system changes thermal density for thermal intensity. Liquid is much more dense than air, and so holds way more thermal energy per unit of volume. Thinking along these lines, it may seem a little more intuitive that a little bit of liquid changing temperature by 3 or 4 degrees can be energetically equivalent to an equivalent amount of air changing temperature by much more. Intuitive, right? Yeah, I know – those heat pumps are like magic. But the point is they work – just like a fridge. Instead of producing energy, you’re moving energy. From the ground to the building in the winter, and from the building to the ground in the summer. Actually, you can move it from a hockey rink surface to a pool, or from the air in the living room to the water in the hot water tank, or ... The trick is – you’re just moving energy around, using the ‘magic’ of a heat pump. The cooling cycle is the same, just running in reverse. The actual install at the hotel will be messy. Houses with a yard are easy – just put in pipes looping around the yard, attach them to heat pump, and you’re home-free. However, since this is a retrofit on a building in downtown Toronto, with no large lawn space for digging – actually, we have ZERO extra footprint outside of the building itself - we’ll have to put in 10 or 12 300-foot deep vertical holes in the laneway beside the building! This is where the series of pipes will go, to enable an exchange of thermal energy with the ground beneath the frost line. Seems like a massive job to me, but the engineer from Clean Energy Developments seemed to take it all in stride. We can get them in nice and close, and angle them slightly, so they fall mostly under the footprint of the building, but we’re still going to have to dig up that laneway. Fingers crossed, we’ll approach our good neighbours at St. Stephen’s Church for the green light on all that digging .... ! Next week – the economics of geothermal. How does it pay for itself? How much carbon does it really displace?? References:

  1. I’ve become so convinced that this technology is the single most viable energy contributor to our real estate that I’ve made a strategic investment in a geothermal startup here in Canada, Clean Energy Developments Inc., and now sit on their Board of Directors. So – in the interest of full disclosure – I’ve a vested interest in pushing geothermal! That said - I’ve only acquired that interest after sniffing out all the carbon-reducing options for this hotel of ours.
  2. What were the other (not-so-hot) options that I’ve discarded? Burning renewables – such as wood chip stoves – may be a nice possibility out in the country, corn-cob pipe in hand and a hound at my feet - but I would need a stove for each room, and let’s not forget that wood source has to be shipped. Combined heating and generation (or co-generation, as it’s known) is a pretty great idea: the heat produced as a by-product of generating electricity, a result of the inherent inefficiencies of the system, is put to use in providing heat. It’s only applicable to much larger buildings, though, or even small communities. I’d have my own generator, basically, and make use of the heat it gives off. Otherwise, it’s down to getting a modern, efficient boiler – preferably natural gas since it contributes much less CO2 per thermal unit than other fossil fuels.

Continue to the next part.

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Galini Beach (anonymous)

What an excellent point, I think that geothermal should be the #1 priority for newly built hotels whenever it is available-accesible. Carbon dioxide emissions are reduced to incredibly low numbers and the cost is not so high to a certain period of time. <a href="http://www.galinibeach.com">Galini Beach Hotel</a> is looking into this idea with great respect.

Written in March 2010

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