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Taking the Fast Track to Efficient HVAC

Posted by Paul Hawken, Guest Columnist

Jun 18, 2018 4:48:10 PM

Why wait for the future? Heat pumps are ready to employ now.

Benjamin Franklin may be the only diplomat to have studied the science of refrigeration. That was in Cambridge, England, in 1758, when he was trying to reduce tensions between King George and the American colony but found time for the lab as well. He and English chemist John Hadley were intrigued by a Scottish scientist’s discovery, made a decade earlier, showing how the evaporation of volatile liquids manifested a secondary effect: cooling. The basic principle is that higher-energy (hotter) molecules evaporate first, leaving the lower-energy (cooler) ones behind.

In Cambridge, the researchers’ equipment consisted of a beaker of ether, a mercury bulb thermometer and a bellows. After wetting the thermometer in the ether, they worked the bellows hard to evaporate the liquid as rapidly as possible. The thermometer recorded the temperature, which dropped to seven degrees Fahrenheit in one trial, and the accumulation of ice solidified the experiment.
Franklin wrote a friend, “One may see the possibility of freezing a man to death on a warm summer’s day.” An exaggeration, but the famous polymath was, yet again, on the right track. Could he have foreseen the consequences of his insight?

Gwyn Pris, professor emeritus at the London School of Economics and Political Science, suggests that addiction to air conditioning (AC) is “the most pervasive and least noticed epidemic” in the United States—where the amount of electricity used to keep buildings cool is equal to what the whole of Africa uses—for everything.

It is easy to understand how this happened: Fossil fuels were plentiful and cheap, no one worried about greenhouse gas emissions or global warming, and cool air was a welcome relief at home and at work. Critics argue AC is one road civilization should never have taken and must now exit. Perhaps, but an exit is not likely. A top aspiration of people around the world—many of them living in the hotter climates of Asia and Africa—is the comfort of air conditioning.

Demographics alone dictate that the world is set for a massive increase in AC demand in this century. One study predicts as much as 33-fold by 2100. China’s experience foreshadows: In the decade-plus between 1995 and 2007, the percentage of air-conditioned homes in Chinese cities increased from 7 percent to 95 percent. China will soon surpass the United States as the leading consumer of AC.
Air conditioning grabs most of the headlines when the subject is conservation and efficiency, but heating is just as susceptible to inefficiency and just as prime for improvement. The building sector worldwide uses approximately 32 percent of all energy generated; more than one-third of that is for heating and cooling. Various bodies have analyzed the potential for increased efficiency and projected the results. All agree on two points: Business as usual generates spiraling emissions from heating and cooling; and maximum efficiency could cut energy use by 30 percent to 40 percent.

Better Energy Efficiency the Easy Way

SUS Symp R Simmer heat pump 9x4 300

Heat pumps like this sewer line-based unit from manufacturer Stadwerke Amstetten offer an emissions-free, green energy-powered way to heat and cool homes.

The means to increase efficiency are at hand and not necessarily high tech. For example, smart thermostats that correlate the temperature setting inside the building with the temperature outside and with actual human occupancy make good sense, but are often missing. Fan speeds are surprisingly important and are often set incorrectly. Heat exchangers to recover heat or cold from air ventilated outside are vital. Retrofitting existing structures with these low-tech interventions is more expensive, but in any new building they should be mandatory. They save money, prevent discomfort and reduce emissions. Combine them with thermostat settings that are a few degrees warmer in summer and a few degrees cooler in winter, and the energy benefits are exponential.

One technology stands out from the rest: heat pumps. These could address the world’s heating and cooling needs and eliminate almost all emissions if powered by renewable energy. Most people have a variation of a heat pump in their homes already: a refrigerator. The working principle is the same. Al refrigerators and heat pumps have a compressor, condenser, expansion valve and evaporator, and both transfer heat from a cold space to a hot one.

In winter, that means pulling heat from outside and sending it into a building. In summer, heat is pulled from inside and sent out. The source or sink of heat can be the ground, air or water. Air-source pumps work best in temperate climates, as efficiency drops off when outside temperatures drop below 40 degrees Fahrenheit. However, newer technology is effective down to 5 degrees if a building is well insulated. In areas such as Scandinavia and northern Japan, ground-source heat pumps are the technology of choice, taking advantage of the Earth’s relatively constant temperature underground.

While cost can be high and efficiency fluctuates depending on local climate, heat pumps are easy to adopt, well understood and already in use around the world. They can supply indoor heating, cooling and hot water—all from one integrated unit. When it comes to efficiency, heat pumps have a singular advantage: For every unit of electricity consumed, an equivalent of up to five units of heat energy is transferred.
According to the International Energy Agency, a 30 percent penetration of the building sector by appropriate heat pumps could reduce worldwide carbon dioxide emissions by 6 percent. This would be one of the larger contributions of any technology now on the market.
When paired with renewable energy sources and building structures designed for efficiency, heat pumps will do more than move warm air. They will move Earth toward drawdown. 


Note: This article is taken from Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming, which describes the 100 most substantive solutions to climate change, as well as their financial histories, the carbon impacts they provide, the relative cost and savings and each solution’s path to adoption

Paul Hawken is executive director of Project Drawdown, a coalition of researchers, scientists, graduate students, policymakers, business leaders and activists who assemble and present the best available information on climate solutions and their beneficial financial, social and environmental impact over the next 30 years. He is also editor of Drawdown: The Most Comprehensive Plan Ever Proposed to Reverse Global Warming. He may be contacted at paulharken@drawdown.org.

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