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  • Writer's pictureJim Gunshinan

Moving Heat

This post first appeared on Sense.com.



Every high school senior taking a course in physics learns the First Law of Thermodynamics: Energy cannot be created or destroyed. The good thing for us is that energy can be transformed. And it can be moved around.

Here’s a simple example of the power of moving energy. Install a solar-powered pump in your yard and use it to pump water into a tank during the day when the sun is out. At night, let the water pour out of the tank by the force of gravity and then through a small turbine, called a micro-hydro system, to produce electricity that powers your lights during the night.

You’ve transformed the sun’s energy into electric energy, the electric energy into mechanical energy, and the mechanical energy back into electrical power. And it’s all powered by the sun, our ultimate renewable energy system that produces no greenhouse gas emissions.

In this article, I’ll introduce you to appliances and systems that save you money by moving energy around and discuss where they work best.


Air Source Heat Pumps Moving energy around is the basic principle behind heat pumps and heat recovery systems. Because of the temperature, pressure, and volume dynamics, you can use a little energy to produce a lot of heat or “coolth.” Because moving heat is more efficient than burning oil or gas, these systems can reduce your utility bills substantially. The annual cost of operating an air-source-heat pump for heating your house is around $1,800, based on average energy rates (gas, electric, and fuel oil). The annual cost for a natural gas furnace, an oil furnace, or an electric baseboard heater is $2,500, $5,100, and $5,300, respectively. When the heat pump is less efficient on the coldest winter nights, most homes will need a backup gas or electric resistance heater. To understand how much you can save, use a home heating calculator developed by Efficiency Maine.

Air-source heat pumps can also take heat from your living space and exhaust it outside, acting as an air conditioner. Check with a trusted contractor to help you decide the most efficient way to heat and cool your house.

Heat Pump Water Heaters Can Save 70% A heat pump water heater is another energy mover. Typically installed in a garage, the water heater will take heat from the air and preheat the cold water into the tank. It will also cool your garage a bit. According to the Department of Energy, using an Energy Star heat pump water heater can save you 70% of the electricity costs compared to the standard electric resistance tank water heater. Depending on your climate and the water heater's efficiency, this can translate to yearly savings of more than $300. Different heat pumps include ducted systems to heat or cool the living space and un-ducted systems that work in individual rooms. A knowledgeable HVAC contractor can advise you on the best for your house.


Newer Homes Benefit from Heat Recovery Systems Another way to move energy around in a home is by using heat recovery systems. Many newer homes are built with heat recovery systems that deliver significant energy efficiency savings compared to more conventional construction. With a more contemporary home that is more air-tight, it is best to control the ventilation of air coming into or out of your house. In older homes that are leaky, the fresh air coming into your home can come through the attic or basement and carry with it things you might not want to breathe, like dander from critters like mice or bats. With a leaky house, you also waste heat in the winter and cool air in the summer.

A heat recovery system is a must in a super-efficient Passive House home that can leak less than one air change per hour at 50 Pascal of pressure (1 ACH50), which is considered very tight. It keeps the air fresh and breathable and minimizes energy consumption. There are two types of heat recovery systems: a heat recovery ventilator (HRV) and an energy recovery ventilator (ERV). Both devices run on a small fan that brings fresh air from the outside and exhausts inside air. They operate on the same principle, though the energy recovery ventilator draws moisture from the incoming air, and the HRV doesn’t. The HRV usually comes as a box of around two or three feet square with four ducts—two on each side. Inside the box, the outgoing and incoming air is separated by a barrier that transfers heat between the air coming in and the air exhausted to the outside. In the summer, hot outside air is cooled by cooler inside air. In the winter, cold outside air is heated with warm air from the inside.

In either case, these ventilation systems can save 80% of the heat or cool that would otherwise be wasted. This means savings of $6 to $230 a year, depending on your climate zone. The systems work best in colder climates and are not recommended for warm/dry and warm/wet temperatures. The equipment and installation of an HRV/ERV can cost about $1,200 to $2,000.

Besides the energy savings, which depend on your climate and heating and cooling efficiency, the main benefit of HRV/ERVs is cleaner air. The Hayward Score was developed by building scientists and health professionals to give you an overview of indoor air quality. An HRV/ERV is a significant part of that score because it provides balanced ventilation.


Capture Heat that’s Going Down the Drain Another clever way to save electricity is by recovering heat from the water you use for showering. A drain water heat recovery system captures the heat from shower water going down the drain to preheat the cool water as it enters your water heater, saving you energy and money.

The typical drain water heat recovery system (DWHR) consists of a copper coil wrapped around the drain water pipe in your basement (which means it doesn’t work for one-story houses). The water coming into your home from your town’s water system or a well runs through the coil, absorbing most of the heat that would otherwise go down the drain. DWHR systems can cost from $300 to $500, not including installation by a certified plumber. The Department of Energy estimates that the payback time for typical homeowners ranges from 2.5 years to 7 years, depending on how much you use it and the temperature of your incoming water supply.

Be an Energy Mover! With all this energy moving around and into and outside our places, it takes a sophisticated energy-saving management system to create comfort. For example, a heat recovery system needs coordination with the other elements of your HVAC system to work most effectively and efficiently. But it’s all based on a simple idea. You can’t create or destroy energy can move it around.


Photo by Arthur Lambillotte on Unsplash.


.Jim Gunshinan is a science writer who covers energy and the environment. He was the editor of No Regrets Remodeling, Second Edition, a science blogger for a PBS affiliate, and editor of a magazine covering green home building and renovation. Jim lives in Walnut Creek, California.


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