Geothermal Heat Pumps
Being fascinated by renewable sources of energy, I like to learn and read about where renewable energy is heading. I should, however, spend more time becoming familiar with the options available in the here and now. One option I know next to nothing about is geothermal energy. This article on geothermal heat pumps caught my eye, so I decided to do a little digging to find out more about this renewable source.
What is a geothermal heat pump?
A geothermal exchange heat pump, also known as a ground source heat pump or GSHP, is a heat pump that uses the Earth as either a heat source, when operating in heating mode, or a heat sink when operating in cooling mode. All geothermal heat pumps are characterised by an external loop containing water or a water/antifreeze mixture (propylene glycol, denatured alcohol or methanol), and a much smaller internal loop containing a refrigerant. Both loops pass through the heat exchanger.
Geothermal heat pumps have the ability to act as either a heat source or heat sink because the Earth's temperature below the frost line remains relatively constant.
During the winter, the fluid collects heat from the earth and carries it through the system and into the building. During the summer, the system reverses itself to cool the building by pulling heat from the building, carrying it through the system and placing it in the ground. This process creates free hot water in the summer and delivers substantial hot water savings in the winter.
Sounds pretty brilliant, doesn't it? Must be a catch ...
Ah, yes. GSHPs cost more upfront than conventional heating/cooling systems. In our two-second-attention-span, profit-obsessed society, anything that costs more money upfront - even if it pays down the line - seems to get benched in favor of the option that saves the most five minutes ago. The more you look at renewable, the more you see that the need for immediate profits is the single biggest barrier to more widespread adoption.
According to the International Ground Source Heat Pump Association, "[GSHP] Investments can be recouped in as little as three years." Plus, GSHPs are very efficient:
The GSHP is one of the most efficient residential heating and cooling systems available today, with heating efficiencies 50 to 70% higher than other heating systems and cooling efficiencies 20 to 40% higher than available air conditioners. That directly translates into savings for you on your utility bills.
GSHPs are also durable, long lasting systems:
The GSHP contains fewer mechanical components, and all components are either buried in the ground or located inside the home, which protects them from outside conditions. The underground pipe carries up to a 50-year warranty.
I'm not seeing a lot on the negative side of the whiteboard. In fact, I'm starting to fall in love with GSHPs:
GSHP systems conserve energy and, because they move heat that already exists rather than burning something to create heat, they reduce the amount of toxic emissions in the atmosphere. They use renewable energy from the sun, and because the system doesn't rely on outside air, it keeps the air inside of buildings cleaner and free from pollens, outdoor pollutants, mold spores, and other allergens.
Are you concerned about the environment and looking to reduce your energy or carbon footprint? Then maybe you should consider installing a GSHP system in your residence. For a list of available financial incentives, check this site out.
I'm going to dig for some less positive information about GSHPs. If and when I locate anything, I'll update this post.
Comments
Thank you for this article!
Posted by: Mixie | December 1, 2008 5:45 PM
Tom C. post mentioned many of the strong points of ground-coupled heat pump systems. But before you make the significant investment in a well field, you should also consider the following.
The heat energy taken from the well field during the winter is free - pumping it into a high temperature sink, however, is not.
Let's make a real world example. Let's assume we need around 28 MBH of heat on a peak winter day.
A 3 ton water source heat pump will provide 27.9 MBh of heat in the form of 90 degree heat and use only 2.27 kWh for each hour of operation. That's only 7,748 BTU of electrical energy for 27,900 BTU's of heat energy!
A condensing gas boiler (efficiency at 95%, say) would need 29,368 BTU worth of gas to provide the same amount of heat how green is that anyway?
But if you look at carbon footprint, you see that in order to produce the 7,748 BTU's worth of energy, the utility had to burn 27,671 BTU's worth of coal.
But that's not the whole story. The natural gas needed to provide you with 27.9 MBH usable heat will release 4 lbs of CO2. The 27.7 MBH of burnt coal will release 6.86 lbs of CO2.
So, the electric intensive ground-coupled system is good for the environment if you live in Washington state and get your juice from hydroelectric. But in Pennsylvania, with all the coal-fired plants? Not so good.
As for the operating cost differential, you are absolutely correct - comparing BTU's to BTU's, your electric use will only be 26% of the energy that that 29,368 BTU's of gas you'll need for the same hour of heating. As long as your kWh rate is 13% or less of the amount you pay for a CCF of gas, your making money. If you pay 12.8 cents per kWh and $1.00 per CCF, for example, you are breaking even between the two energy costs.
Now, the ground-coupled system does have two more expenses. One is pump energy for moving the source water to the heat pump and back to the wellfield. This is not large - it will bump your peak hourly kW to 2.5 kW or so - meaning that as long as your $/kWh is less than 12% of your $/CCF, you make out.
As for the investment? It's a sizeable one.
Posted by: John | February 20, 2010 6:03 PM