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


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.


Lawn Watering should be avoided. Green grass looks nice, but the water consumed is likely your largest regular outlay of water, and you need to do it regularly to keep the grass green. By not watering your lawn, your grass will stop growing, meaning less need to mow it which saves time and fuel if you’re using a gasoline-powered lawnmower. Your grass will not die from lack of watering, it simply goes dormant until it rains. If you water your lawn regularly it may be the largest portion of your water bill, in some cases 75-90% of the bill may be coming from simply watering the lawn.

However if you must do so, water in the evening to reduce evaporation losses, install an efficient sprinkler or underground watering mechanism to reduce water needs and water less often and for longer periods so the grass develops deeper roots, as frequent shallow watering lead to shallow roots and less water uptake.

Hot Tubs and Swimming Pools are also large users of water, especially if you need to add water to them frequently. These luxuries are best avoided, especially swimming pools which can require hundreds of dollars of water to fill, not to mention the chemicals and time and additional expenses in heat and electricity required to operate and maintain them. They have recently become popular in some areas thanks to Covid-induced social distancing, but the virus will not last forever and the cost of maintaining these will. If you’re considering installing a hot tub or swimming pool, consider using that money to buy solar panels or battery storage or an EV instead.

Rainwater usage in the home may be a possibility. You can collect it using rain barrels or other tanks and use it for non-potable uses, watering plants, lawn watering, and so forth. This is legal in most but not all locations. Balance this against convenience and water cleanliness concerns (you don’t want to use it for drinking or cooking). You may also consider using collected rainwater for watering a fruit or vegetable garden, though make sure the containers you use don’t leech harmful chemicals.

Hot Water Considerations

Hot water is a luxury that we don’t think about except when it’s not working or we need to replace the hot water appliance. There are 4 main types of hot water heaters:

Natural Gas: These are devices that burn gas to heat the water. These come in tank and instantaneous heating units. These are typically cost effective to purchase, long lived, and rather efficient.

The tank units come in chimney and powervent (and rarely, direct vent). The powervent is more efficient than the chimney vent due to reduced indoor air losses due to the perpetual stack effect caused by a chimney. Power vent requires electricity while the chimney vent typically does not, but the natural gas savings outweigh the power used by the powervent units. If you can find a water heater model that uses outdoor air for combustion then you will save extra on indoor air heating/cooling but these are uncommon.

Instantaneous hot water heaters are more expensive, reasonably long lived, and more efficient. However, the maintenance requirements can negate the savings, the extra purchase price may not pay for the fuel savings, and if you take advantage of their tankless nature and use more hot water than the tank unit allowed, you may actually use more fuel than you’re saving (and water), leading to a net loss of environmental benefits. Also tankless water heaters can have their quirks — you may need a high enough flow rate to get any hot water at all, they may have a lower than expected maximum flow rate, it may take a while to get hot enough (meaning extra water waste), and the dreaded cold water sandwich.

Electric: These devices heat the water with high energy resistance heating coils, and they also come in tank form and instantaneous heating units. These are typically very cost effective to purchase, long lived, and very efficient.

The tank units heat the water with virtually 100% electrical efficiency, as almost all the energy is converted to heat and the water is stored in the tank. However, electrical heating is often very expensive because electricity typically costs several times as much as natural gas. Also electric hot water heaters often take much longer to heat the water, sometimes 3-5 times as long as natural gas (known as the recovery rate). The environmental impact of electric hot water can be much larger then natural gas if the electricity is not generated by renewables. The heating may be 100% efficient, but generating that power is far less efficient, often at 30-50% plus line losses. A natural gas unit burns the fuel and scavenges the heat directly while a power plant burns the fuel and discards the heat then sends the power to your home where it is used electrically, meaning the round trip efficiency can be in the 20-40% range (which also helps explain its much higher cost than natural gas per joule of heat).

Instantaneous electric hot water heaters are also available, but have the same caveats as natural gas instantaneous units, plus two additional complications. They can often have even lower maximum flow rates then their natural gas cousins, and the amount of power needed to operate them leads to huge peak loads, far beyond what a home-charged EV draws. This can tax your local grid and could never be handled by a Tesla Powerwall or other home storage battery. If too many people in a neighborhood have electric instantaneous hot water it would lead to grid problems if they shower or use hot water at the same time. Hence these units are best avoided.

Heat Pump: These devices heat the water using a heat pump, utilizing a principle similar to your fridge but operated in reverse. They only come in heated tank form. These are typically quite expensive to purchase, long lived, and extremely (200-300%) efficient. However, repair costs can be high if you ever have a breakdown, and they are a niche product which may be hard to find in some countries.

They work by taking heat from the room and depositing it into the water in the tank. In summer time they provide some free air conditioning and dehumidification and in winter they add a load to your building. They also regenerate much more slowly then natural gas and often even slower then electric resistance heaters. However, their operating cost is often similar to natural gas and they use 1/3 to 1/2 the energy of an electric resistance water tank. They are the most environmentally-conscious choice, especially combined with renewable electricity.

Stay tuned until next week for Part Nine – Solar Hot Water and Additional Hot Water Considerations


 



 


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