Propane freestanding stove for back up heat or propane generator powering ducted heat pump
Calum Wilde| Posted inEnergy Efficiency and Durabilityon
I’m wondering what setup would use less propane/energy? Upfront costs is also a concern. The propose of the system would be to keep a house warn in the even of extended power outages. We’ll likely be installing a generator of some size for lights, fridges, etc. Would the “efficiency” of a heat pump outweigh the loses of generating electricity with a propane generator to run it vs just directly burning the propane in a free standing stove?
有能力做的stove would of course also be a bonus, but the merits of that are another question that’ll be up to us to consider.
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Replies
Calum,
A lot depends on how you heat the house when the power is on. If you can power whatever system you already have, there isn't much point installing another largely redundant one just for outages.
Around here that typically means power to the electric resistance baseboards, or more recently heat pumps, although most houses have wood stoves. Anyone with a propane generator usually also has piped propane to a barbecue for cooking.
Worth remembering that you go through an awful lot of propane in a hurry even just running small loads on something like a 17kw generator.
The house already has the heat pump.
Calum,
I'd hook it, and a few other circuits up to a propane generator.
Since generators can and do fail to start, any true backup means something that requires no electricity. This tends to be a stove or through the wall vented propane heater.
Akos,
Our fire department, community hall and the three restaurants in our community all use propane powered Generec generators. They could conceivably fail, but they are pretty reliable, do diagnostic tests and automatic start-ups, and can be monitored remotely.
We use a 7000 watt Honda gasoline powered inverter generator when the power goes out. It's wired into an outdoor receptacle that connects to the electric panel. It runs our heat pumps. But when power goes out, you need more than heat. You need to keep food cold, to be able to cook, in rural areas, to run a well pump, etc. Our generator runs the induction cooktop and everything except the electric oven, although if we turn on the resistance water heater, we need to limit other appliances.
I keep around 20 gallons of gas in a garden shed. If it looks like power will be out for more than a fay or two, we limit generator use to a few hours a few times a day. Twenty gallons will.last a week if we're careful. Before gas gets stale, I put it into a vehicle and replace it.
Stephen has a very solid point, you need electricity for lights and charging phones or listening to the weather on the radio and whatnot... BUT... just because I like numbers:
- Propane has 91,500 BTUs per gallon.
- The Westinghouse iGen4500 provides 3,330 running watts on propane and based on my calculations, burns 0.209 gallons of propane at 25% load to generator 0.832Kwh.
——这意味着0.209加仑的丙烷(19132BTU) generated 0.832KwH electricity (2,838 BTU).
Assuming a COP of 3.0 on your heat pump... that means 19,132 BTU of propane would have ended up generating 2838 x 3, or 8,514 BTU of heat. If the efficiency of your propane space heater is greater than 44.5% (8,514/19,132) - then purely for space heating, using a propane heater would be a more efficient use of propane.
Generally speaking, changing the form of energy once (chemical-->heat via propane heater) will almost always be more efficient than changing the form of energy multiple times (chemical-->mechanical-->electrical-->mechanical-->heat) via generator+heat pump.
You're correct, but nobody cares about efficiency when the power is out. A typical propane heater , like the Rennai, is about 80% efficient. But as I said above, you still need a generator to run all the other stuff. So you might as well use the generator to run your heating appliance, whether it's a heat pump, furnace or boiler.
Totally agree, but it was a fun exercise. :)
The fewer times you change the form of energy, the less you'll lose along the way. That's why it's better to burn fuel directly than it is to use electric resistance heat if the electricity was generated from the same fuel source you could have used for heat directly. Things get a little more complicated when you're running a heat pump, but keep in mind that a typical internal combustion engine running on gasoline, propane, or natural gas will be around 16% efficient -- and even less when running at less than full load. Even when running a heat pump, you'd probably be better off burning the fuel for heat directly if efficiency was your only concern.
Note that "only concern" part. I absolutely 100% agree with Stephen here: when the power is out, efficiency IS NOT a primary concern. Running what you NEED to run is the primary concern. Electricity can run whatever you normally use for heat, and it can also run your fridge, lights, and anything else you need. That makes a generator a whole lot more flexible, and a whole lot more useful, than a simple heater would be. I would go with a generator for that reason alone.
Generators that are properly maintained are very reliable. The issue is that typical homeowners don't maintain their generators. There are certain maintenance items that are important, such as periodically running the unit, and changing the oil at least once a year even if you don't use the generator that year. I also recommend using full synthetic oil in generators. The rule is "change the oil every 100 hours of operation, or every year, whichever comes first". The other rule is "run the unit 30 minutes weekly, or at least long enough to get up to operating temperature". Do those two things and you'll be in pretty good shape. If you stuff the generator in your garage and tegb don't touch it again until the big ice storm five years later, don't be surprised when it doesn't want to start.
Bill