I live in a 100 years old house in central Denver with natural gas boiler driven steam heat radiators (the steam heat boiler was originally coal fired, which is not an option now, then converted to gas, and then replaced) and a swamp cooler. (I'm looking at this now because my 24 year old swamp cooler is replaced for the first time today.)
Is this the best choice from a cost perspective?
Yes.
Is this the best choice for the environment?
Probably, although a heat pump is quite competitive from an environmental perspective and will grow more attractive as the power grid in Colorado becomes greener over the next decade or two.
Cooling
In Denver, swamp coolers (a.k.a. evaporative coolers) generally cost less to operate than heat pumps, especially during the cooling season, in part, because Denver's humidity in the summer is low. Swamp coolers use significantly less electricity than air conditioners, often saving 60-80% on energy costs. Heat pumps are about 50% more efficient than central air conditioners, but swamp coolers still draw 20% to 40% less electricity than heat pumps. See here and here. All three cooling costs are powered by electricity, so the relative energy costs are indifferent to the price of electricity.
Swamp coolers do use some water than heat pumps and central AC systems don't use. But this is pretty negligible in terms of the cost of well under a dollar a month (you pay for tap water at prices on the order of a few dollars per 10,000 gallons, and a swamp cooler uses less than 900 gallons a month and is only operating about five months a year, so the water costs are less than $3 per year). This is also pretty negligible in terms of the swamp cooler's share of total water consumption. In contrast, water for landscaping uses about half of our water consumption despite the fact that we have only a couple hundred square feet of lawn.
The maintenance costs of a swamp cooler are a little bit greater than for central air conditioning and heat pumps, however, because they have to be started up every spring, and shut down every autumn (filter replacement costs are comparable for central air condition and swamp coolers), but this can be a DIY maintenance job if you are up for it, and the costs is significantly smaller than the energy cost savings involved.
Also, a swamp cooler is much simpler and less expensive to repair than an air conditioner or heat pump because it is mechanically simpler. A swamp cooler has one simple electric motor that runs a fan, and the water flow is controlled by a float system similar to one in a residential flush toilet. A broken swamp cooler take much less time, much less skill, and much less expensive parts to fix than a broken air conditioner or heat pump. Higher end and newer swamp coolers are also more resistant to rust than older models.
And, the up front installation cost of a swamp cooler is lower than the installation cost of an air conditioner or heat pump, even without utility or government incentives, although rebates from Xcel Energy to encourage swamp cooler use improve this comparison.
A heat pump or central AC can reduce temperatures a bit more than a swamp cooler does. But this only matters at all for maybe the ten or twelve hottest days each year, and even then, with a good quality swamp cooler like the one we are having installed, the difference is tolerable and isn't huge. And, the humidifying effects of a swamp cooler also make a home more comfortable in the very dry, almost high desert conditions of Denver summers, relative to air conditioning or a heat pump, once you get used to it. Both a swamp cooler and central air conditioning do suck in the sometimes polluted outdoor air into the house on low air quality days which we get plenty of in Denver in the summer. But a swamp cooler does a better job of filtering that air than a typical central air conditioning filter does.
Environmentally, apart from energy costs, swamp coolers are also better, because they don't need the chemical fluids required for heat pumps or central AC to move heat outdoors (or to suck subsurface cool temperatures into your home).
Heating
In Denver, a gas boiler steam heat system is about 25% cheaper in fuel costs (at current natural gas and electrical prices from Xcel Energy which is about $1.26 per therm for natural gas and 20 centers per KwH for electricity) than a geothermal heat pump. See this calculator. In fact, this is the least expensive heating option of all of the possible alternatives, including gas forced air furnaces, wood stoves, pellet stoves, heat pumps, heating oil, kerosene, propane, or electric baseboard heating.
A couple of years ago, we replaced our old natural gas boiler (which had been converted from the original one hundred year old coal fired boiler), which is much smaller, is easier to operate and maintain, and is slightly more efficient, than our old one. It is much less expensive to replace a natural gas boiler for an existing steam heat system than it is to install a new heat pump system of any kind in a building that previously had a steam heat radiator system. I suspect that it would also be cheaper in new construction, but the installation cost advantage in new construction would be much less decisive.
Heat pump installation costs also have to be compared to the combined installation cost of both the cooling system and the heating system, because it does both jobs. And, in new construction for a new subdivision, using a heat pump and an electric water heater, instead of natural gas heat and other natural gas appliances and water heaters, avoids the substantial costs of building a subdivision with deeply buried natural gas pipelines serving each home. So, again, when building new construction homes in new subdivisions, the installation cost economics for heat pumps v. natural gas heating are much different than they are with existing construction in which every home is already served by natural gas pipelines.
The steam heat boiler does consume water that the heat pump or a gas forced air furnace would not (although many gas forced air furnaces have a humidifier built in that uses considerably more water than a steam heat boiler per year), but this too is negligible in both cost (less than a dollar per year) and the amount of tap water used (probably less than 90 gallons a year), since it is an almost closed system that recycles the water and only loses a little bit each cycle to evaporation at the boiler point. Our steam heat boiler has a water filter that needs to be replaced twice a year (because a lot of our pipes are old and made of galvanized steel and have some rust in them) at a price comparable to the cost of an air filter for a gas forced air furnace (which is not necessary in a heat pump) but this is also negligible compared to the differences in energy costs.
In terms of the in home results, radiator based steam heat is much nicer than gas forced air heat, because it doesn't dry out the air (an issue that a built in humidifier only partially addresses) and doesn't drag polluted outdoor air into the house on poor air quality days which Denver has plenty of, even in the winter.
Historically, heat pumps have been used primarily in the South in the U.S., where high humidity during long hot summers makes evaporative coolers useless in the summer so homes need either air conditioning or a heat pump to be comfortable in the summer, where it doesn't get that cold in the winter so the amount of heating needed is modest enough that infrastructure costs necessary for natural gas or heating oil based heating systems didn't make sense, and when heat pumps were less effective than they are today at heating homes in the winter. Since the infrastructure and installation costs of central air conditioning and a heat pump are similar (although geothermal heat pumps are a bit more expensive to install than central air conditioning), the marginal cost of a heat pump over the central air conditioning that you would otherwise need in the South was modest (technologically a heat pump is basically an air conditioner that you can run backwards), it made sense there to heat homes with a heat pump. Also, since the amount of heating degree days per year in the South is pretty modest, the greater summer cooling efficiency of a heat pump relative to central air conditioning pretty much pays for the energy costs of providing heat on infrequent and mild winter days in the South. And, since the amount of energy needed for fuel for the winter for a heat pump in the winter in the South is pretty modest, saving a little money with a cheaper fuel was relatively less important than saving money by reducing the installation costs and having more energy efficient summer cooling.
Modern heat pumps, especially geothermal heat pumps, that are well suited to colder climates and designed for them, are now widely available. But this wasn't the cost effective option when Northeastern homes overwhelmingly were heated with heating oil, and Midwestern homes and western homes in places with cooler climates were overwhelmingly heated with natural gas. And, as noted above, the economics of heat pumps are a lot more favorable in new build construction, especially in new subdivisions that dispense with creating natural gas pipelines to every home, than they are in homes where the old heating and cooling system needs to be torn out and replaced by a new heat pump (especially in homes with boiler based heat rather than forced air heating and cooling ducts).
Environmentally, at this point, it is a bit of a wash.
Natural gas in a home boiler burns almost as efficiently and cleanly as in a utility scale natural gas power plant (and is more efficient and less polluting at turning natural gas into heat because it doesn't lose energy by converting heat to electricity, losing electricity in transmission lines, and converting electricity back to heat again). And, natural gas creates much less air pollution than coal or firewood or pellets or propane or kerosene or heating oil in a home boiler, and creates less air pollution per unit of energy used than a utility scale coal fired electrical power plant.
But the air pollution caused by generating the electricity in the grid, in part from coal, and less efficient (for heat production) natural gas, is offset by the fact that about 45% of the electricity in the grid comes from hydroelectric, solar, and wind power in Colorado.
Natural gas also creates toxic pollution in the ground in the extraction process (a significant share of which comes from fracking), and that toxic extraction process is used to provide 100% of the fuel for a home natural gas boiler, but only less than half of the fuel for the power grid. But, the mining done to extract the coal that is the source of a still significant share of the electricity in the Colorado power grid, is much more toxic and creates far more harms to workers and the public from the extraction process alone (ignoring the air pollution) than natural gas extraction does (even considering the harms of fracking).
As more of Colorado's power grid comes from renewables, and less of it comes from natural gas, and coal is eventually virtually eliminated as a source of electricity for the Colorado power grid, electricity will eventually be greener than natural gas, but this will still be partially offset because a home boiler still generates heat with less energy than the power plant generating the energy needed for a heat pump does. So, even as the grid gets cleaner and tilts a little more in favor of heat pumps relative to a natural gas boiler, the environmental difference is still going to be pretty modest.
Home Based Solar Power Considered
Last year we got a detailed bid for the solar power system that our particular home could support in terms of power generation capacity and cost.
In terms of the cost of the electricity, it could have met almost 100% of our current electrical demand at a cost that would be about the same as buying electricity from Xcel Energy at the prices we are paying for electricity now, over the next twenty years (with substantial Xcel energy rebates and government tax credits). So, this wouldn't have changed the cost calculus discussed above, although having our own solar power with some sort of battery storage would have given us a hedge against rising electricity prices from Xcel over time.
But, given the rapid rate at which solar panel prices are falling, and the rapid improvements that are in the works in battery technology, it might be cheaper to get a solar power/battery system and the product might have better quality a decade or so from now, even without rebates and tax credits.
And, the fact that our house is a hundred years old and has roof framing that is almost surely not up to current building code standards was also a consideration. The rooftop solar power installation might have disturbed that by putting more of a burden on the roof or just damaging the existing roof framing in the process in a manner that in a worse case scenario might have required a major structural repair job to bring our roof framing up to current building code standards, in a half duplex where that kind of repair would also have to involve the owner of the other half of the duplex.
Solar power would have insulated us from temporary disruptions in our electrical service from Xcel (which typically range from a few minutes to a couple of hours and happen at most two or three times a year, with outages of more than a couple of minutes only once every few years).
It would have been environmentally cleaner, of course to get 100% of our electricity (on average) from solar power, although the environmental benefit of this would be reduced over the next couple of decades as the Colorado power grid gets greener.
If we were building this home new at this time, we would probably have opted for solar power, particularly if it was in a new subdivision that didn't have natural gas pipelines in place to every home. But as this stand, the benefit of getting rooftop solar power was not decisive enough for us to justify the time, trouble, and disruption to our lives in connection with the installation work and any possible follow roof repair work that might be needed, to justify making the change now.
3 comments:
"years old house" should be hundred-year-old house. Compound noun.
Hyphens are almost never material, and their use is almost never mandatory.
My experience with international conversations in English always reinforces my preference for hyphenating compound-nouns, reducing potential confusion frequency.
Here in Miami, hot and humid mostly, at sea level & flat, lots of roof solar panels, no swamp coolers, lots of AC. Modern housing environmental control is remarkably inefficient for overall populations, despite technological progress, and this has spread globally with western-style development. Sometimes I think we should invest in high-tech bamboo/wood-burning, being non-fossil & solar derived. Millions of acres of forest timber & pulp, much susceptible to seasonal wildfires, could be used, (perhaps fermented to get wood-gas, piped with petrol pipelines), some biochar & wood ash remaining to improve & stabilize the soils. That is global long-term, whereas you're focused on local short-term, of course.
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