Improving The Efficiency Of Your Home — Series 2: Heating, Cooling, (Hot) Water — Part Three

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Buildings

Published on January 29th, 2021 | by Barry A.F.

January 29th, 2021 by  


One of the ways to slow the advance of climate change is to reduce your personal carbon usage. While we can’t efficiency our way to climate neutrality, we can buy ourselves time by slowing the rate of carbon emissions and conservation, as Negawatts are often the cheapest form of clean energy available (and the least polluting). Also when you have less energy to replace, it’s cheaper to do so (i.e. if you cut your energy use in half, then only half the renewables are needed to make it sustainable).

Our homes can seem like a monolithic entity — they need heat and or cooling, they use water and heated hot water, they consume electricity, and need lighting and plumbing. But the structure plus our actions can alter how much carbon is produced by several orders of magnitude. Two equivalent homes standing side by side could have 5 to 20 times the difference in carbon pollution produced in daily operation. A 100+ year old leaky home with inefficient appliances and high electricity use creating dozens of tons of CO2 a year can stand next to a Passivhaus or Net Zero home, which has very low or even no carbon emissions whatsoever. And there is a huge continuum in between these extremes. Many existing homes that are inefficient can be upgraded to various degrees to reduce their carbon footprints.

This will be a four-part series:
Series One: Insulation And Air Sealing
Series Two: Heating/Cooling And (Hot) Water
Series Three: Plug Loads
Series Four: Building For Net Zero Or Better

The standard disclaimers apply, all advice is for informational purposes only, CleanTechnica is not responsible for any damages caused by inaccurate information or following any information provided, consult professional expertise before making any modifications to your home, all information is subject to change as our knowledge evolves, and the coffee may be hot.

This article series is focused on detached and semi-detached homes, but many of the concepts are applicable to all building types.


Geothermal is a heating and cooling system that uses the ground to heat and cool your home, as the Earth is typically 5-10ºC year round below the frost line (depending on location). It is used as a giant thermal mass, sucking heat out of the planet when you need warmth and a mass to put heat into when you need air conditioning. And it is often considered eco-friendly.

Unfortunately it’s an expensive headache and often does not perform to its rated specs. It is rather common for system efficiencies to be stated without all the electricity used to run the pumps/electronics, the ground can get saturated and fail to keep up on the coldest or hottest days when you need them most (then have trouble recovering since you’re still trying to keep using the Earth before the saturation dissipates), the efficiencies can fall to electric resistance heat or worse on extreme temperature days, the installation cost is typically atrocious, and the maintenance/repair costs can be astronomical. And if oversized to (hopefully) prevent saturation, then you’re paying a lifetime energy penalty in running the system.

But geothermal has a cult following, and it is very likely its defenders will show up in the comments below and state everything written is wrong or how they beat the odds and are saving so much energy, but it is mostly hype for those who want to believe that other technologies cannot compete. Here is more information if you have a membership to read it.

If you are considering installing geothermal, do run the numbers with an expert who has experience in the real world performance of these systems (and not rose-colored glasses), but the payback period is probably much longer than you will live if there is payback at all. Especially compared to a high efficiency home with an air source heat pump or other eco-friendly heat source. Or with an efficient or Net Zero designed home with solar panels. There can be some edge cases or mild climates that change the calculus.

That said, if you are considering purchasing a home that already has a geothermal system installed, you would be wise to get an energy audit done and compare the results with the bills from the last few years from the previous owner, who should be able to provide a copies or can get historical bills from their local electrical utility. This will tell you how well the system is doing compared to its theoretical energy requirements.

Electricity For Heating

This is the best medium for heating your home from an environmental perspective. It can be renewable, but cost-effectiveness can get tricky. There are two types of electrical heat: resistance and heat pump.

Resistance heating is the simplest. It is a larger scaled version of space heaters that most people in cold weather countries are familiar with. This type of heating gets very pricey very quickly, as electricity often costs 2-10x what natural gas costs per unit of heat. Hence this type of heating is typically best avoided unless your electricity costs are incredibly low.

Air source heat pumps are the preferred method of heating electrically (and typically also handle cooling, covered later). They work on the same principle as an air conditioner or fridge, just in the opposite direction. They pump heat from a colder zone (outside) to a warmer zone (your home). They are typically over 250% efficient, but efficiency varies and older units can be far less efficient then newer ones. They are not breaking the laws of thermodynamics or the law of conservation of energy, but instead of converting electricity into heat they only move it, hence they can exceed 100% efficiency. If your electricity costs about 2.5x the cost of natural gas heat per unit, then the cost would be a wash. Heat pumps have a few wrinkles — the less the temperature difference between indoors and outdoors the more efficient they are, they are currently less common than fossil fuel-based furnaces, and in very cold temperatures they can have trouble keeping up. If your outdoor temperatures often go below -30ºC in winter you might not be the best candidate for a heat pump, though the technology is continuing to improve and you should revisit this option in the future.

Considerations For Heating

For all heating solutions, figure out your current efficiency and do the math based on your bills to determine what your savings potential is if you upgrade to higher efficiency heating. Enlist an efficiency professional if required, and if you did get an energy audit or consulted someone for the insulation/air sealing from the last article, this should be part of the package. And enlist a potential consultant on upgrades.

As comfort is the primary goal of heating, the units ideally should be sized for the load of the home/unit. If vastly oversized, you will get blasts of hot air heating your house, then cold spots, and often colder rooms. The constant on/off cycles also ages equipment more quickly leading to premature repairs and eventually heat exchanger cracks or cascade failures where you have to do constant repairs until you have blown a lot of money and then decide to replace the system. It is considered good practice to oversize units by about 40% to not onlyu balance comfort but also to handle temperatures below the 99% design temperature. But avoid going too far beyond 40%, and don’t assume old equipment was properly sized when upgrading/replacing, as it likely was not.

Retrofitting radiant floor heating is typically a waste of money if the house is properly insulated. It is expensive to install, typically cannot be used for cooling, and electric versions will be very expensive to operate. There are some cases where it works reasonably well.

Stay tuned till next week for Part Four – Cooling your home 
 


 


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About the Author

I’ve had an interest in renewable energy and EVs since the days of deep cycle lead acid conversions and repurposed drive motors (and $10/watt solar panels). How things have changed. Also I have an interest in systems thinking (or first principles as some call it), digging into how things work from the ground up. Did you know that 97% of all Wikipedia articles link to Philosophy? A very small percentage link to Pragmatism.  
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