Oh, burning fossils in a modern combined cycle facility with some district heating at say 60% efficiency, then using that energy to run a heat pump at 300% COP, is waaaay better than burning the same fossils at home directly at 90% efficiency.
Add to that that electricity is never 100% from fossils, anywhere.
Electricity is relatively clean and 300% COP makes it a total no-brainer. Only politics is limiting the mass adoption of heat pumps. Politics include selling natural gas 3 times cheaper per energy than electric power.
Oh, burning fossils in a modern combined cycle facility with some district heating at say 60% efficiency, then using that energy to run a heat pump at 300% COP, is waaaay better than burning the same fossils at home directly at 90% efficiency.
here the relatively old coal fired powerplant is 47% efficiency when making just electricity, it also supplies district heating so when the mix is right efficiency is ~90%
Am I correct that they both cool and heat?
Reversible air to water heat pumps can, but they will need fan coil units to also do cooling. They also need radiators with low enough thermal resistance to the room they can heat it to 20c with ~45c water temperature on a cold day.
Where does the heat energy come from?
A heat pump, pumps heat. For an air to water heatpump, the heat comes out of the outside air. As long as the delta-t is small enough this is more efficient than just resistive heating.
If it's electricity, using electricity for the actual heat is just insane with the price increases that I understand are coming.
Everything is getting expensive.
I like using natural gas for heating, I have a dual fuel system with a heat pump too but when it gets colder out I prefer the warmer air from the gas heat and I really dislike the defrost cycles that the heat pump does in cold weather. I need gas to my house anyway since I use it for cooking, electric resistance stoves suck and I've never heard of a heat pump stove. Another big advantage of gas heat is I can run my furnace along with the rest of my house on my little 2kW inverter generator during power outages which almost always happen during the winter storm season. I'd need a much larger generator to run my heat pump.
Yes, a hybrid like that makes a lot of sense and has a potential of reducing heating cost and CO2 footprint by some 50-70% easily.
In heat umps, where does the heat come from, how is it made available?
A heat pump is identical to an air conditioner with one difference, it adds a reversing valve and a second refrigerant metering device that enables it to reverse the refrigeration cycle. In the summer it works as an air conditioner, refrigerating the inside of your house and exhausting the heat outside. In the winter the cycle reverses, the evaporator becomes the condenser and vice versa, it refrigerates the outdoors exhausting warm air into your house. Refrigerant boils at a very low temperature so it is able to extract heat from the environment even when it is very cold outside.
Technically speaking, an air conditioner is a type of heat pump already, it works by pumping heat from inside your house to the outside. The name "heat pump" is just usually reserved for the reversible systems in order to differentiate them from air conditioners that provide cooling.
If you have a decent understanding of physics already, look up "refrigeration cycle" if you are not already familiar with the principal and the pieces should all fall into place, it's simple physics.
I really dislike the defrost cycles that the heat pump does in cold weather.
On principle, for the meltwater or for the interruption? Most of the systems here recommend a buffer tank any way.
Many years back, there was a heat pump in development that embedded a wire inside the outdoor coil and energized it with a burst of high power RF to cause some frost to flash to steam and blow out the remaining frost, so the defrost cycles only took a short time and did not use much energy. Not sure what it would take for it to get to market.
What if the electricity goes out, how would you prevent your pipes from freezing in that situation?
Cheapest solution to add to an existing building is a hot water recirculating pump, uses something like 10W to circulate hot water back into the cold at the faucet farthest away from the water heater (will need one for each "branch" in the plumbing). It doesn't even need to run all the time, making it trivial to run from batteries with a thermostat on the pipe switching it on as needed. The thermal capacity of the water heater will last well into days or weeks depending on how well the pipes are insulated.
What if the electricity goes out, how would you prevent your pipes from freezing in that situation?
Electricity is needed for circulation of heat carrier liquid in ANY kind of system, unless you are heating your house with fireplace. In case you are afraid of electricity or heat source going out - fill your heating system with antifreeeze.
With a buffer and 50% propylene glycol that's quite a bit of extra money.
I really dislike the defrost cycles that the heat pump does in cold weather.
On principle, for the meltwater or for the interruption? Most of the systems here recommend a buffer tank any way.
I think we may be talking about different things. If you mention "heat pump" to an American they will assume an air source heat pump, with a ducted forced air system indoors. In heating mode the outdoor coil gets much colder than ambient and depending on conditions it can turn into a solid block of ice. It is not easy to sense when this happens, at least with traditional systems so what they typically do is initiate a defrost cycle on a timed schedule, once a defrost cycle is initiated the fan in the outdoor unit turns off and the reversing valve switches into cooling mode which then draws heat from the house (by blasting frigid air out the vents) for a few minutes to heat up the outdoor coil until a thermostatic switch activates terminating the cycle. Even with the outdoor fan shut off, air conditioning when it is 30F outside is ferociously efficient and it is really noticeable. A standard heat pump installation will have perhaps 10-20kW of electric resistance heat that comes on during the defrost cycle and that will take the edge off it but even that is not enough to completely overcome the cooling and make the air from the vents warm. With a dual fuel system like I have I try to set the balance point so it just never runs a defrost cycle because the gas furnace takes too long to fire up for it to work well to start it up during the defrost.
What if the electricity goes out, how would you prevent your pipes from freezing in that situation?
Electricity is needed for circulation of heat carrier liquid in ANY kind of system, unless you are heating your house with fireplace. In case you are afraid of electricity or heat source going out - fill your heating system with antifreeeze.
A gas furnace or boiler and circulation pump can easily be run off a compact suitcase style inverter generator like I have. A heat pump is going to need several kW and will be 240V, which in North America in particular is going to be a much larger generator.
Modern air source heatpumps, those that are actually designed for heating around or below freezing point, for some last 10 years, have improved defrosting quite a bit.
It's mostly a software thing.
From physics perspective, defrosting is not a problem; when condensing outdoor air from gaseous phase to liquid then ice, the latent energy comes in our advantage. When defrosting back to liquid (+ a bit of steam), we just lose that part of energy we already gained. From physics perspective, the result is the same as running continuously in a perfectly dry air with no defrosting need.
In practice, there are losses in the defrost process but that subjects it to optimization. If you run 5 minutes of defrosting every 30 minutes "just in case", it's going to be a huge loss of COP. First, it's important to reliably detect the need of defrosting. This is not too difficult, look at the difference between the evaporator coil temperature and outdoor air temperature for example, if layer of ice is blocking the airflow, this difference increases. The key is to place the sensors appropriately, or even use multiple sensors, test the shit out of the system in different conditions and finetune the algorithm.
Then the defrosting itself, it's best to use as high power as possible to do it quickly, but then it's important to stop the cycle as soon as all the ice is gone. Any excess time spent heating the outdoor air is waste.
The Big Names, mostly Japanese but also some Korean and Chinese, have managed to solve this problem pretty well. There are occasional issues like the well-known Mitsubishi Electric suddenly delivering a new series of "high-quality" "Nordic optimized" heat pumps where significant percentage has completely broken defrosting logic, but such failures happen on any field time to time.
But in reality, in modern machines, the COP drops like 0.2-0.3 units in frosting conditions, but no more than that.
And be aware that the need for defrosting begins already above the freezing point, around 3-5 degC, because the thing cools the outside air so the evaporator coil runs somewhat cooler.
Very cold air cannot hold much moisture so the amount of defrosting is reduced in very cold weather.
With a buffer and 50% propylene glycol that's quite a bit of extra money.
You don't need to go that far, look up the difference between "freezing point" and "burst point". At freezing point, the solution starts becoming slushy, but you need to go down to "burst point" for it to actually damage pipework. 20-25% gets you far.
It's still expensive if you have large storage. I for example have a 1200 liter buffer tank. No antifreeze for me.
Besides, antifreeze worsens the thermal transfer properties of the water, with heatpumps this translates into slight COP penalty. Water pumping losses also increase due to higher viscosity; the reason why ground source systems which
need antifreeze use ethanol which is less viscous than the glycols.
Then, in reality you may have a leak or need to do maintenance on the system. Then recovering the fluid and putting it back is PITA compared to just using water.
I prefer putting the money spent in antifreeze into the insulation, instead. Because finally, if you are without power for many days, domestic water pipes are going to burst anyway, you can't put antifreeze there. The same strategy works for both domestic water and heating water pipes: 1) keep inside insulated envelope of the house, 2) properly insulate pipes that are not within the house, 3) use backup heating sources, 4) in case of a long outage and no backup heating available, drain the system as the last resort.
To get the most efficiency out of a gas boiler, it is necessary to recover the most heat possible from the burning gas, which means to cool down the flue gas to the maximum extent possible before venting it. Modern boilers will do this more efficiently than older designs. You will need to research the specifications of what is commonly available on the US market. This is a big deal in the UK where hot water to radiators is a common heating design.
The other way to heat houses more efficiently, again common in the UK, is to fit thermostatic valves to the radiators. In unoccupied rooms you can dial down the temperature to save fuel. You also want to make sure the central heating thermostat is located in a commonly occupied area so the temperature is related more closely to the comfort of the occupants.
What he said, basically.
60% is utterly dire by modern standards, 90-95% is now normal so long as the flow and return temperatures aren't too high (65 C and 45 C being reasonable for a modern condensing boiler). Sometimes on a retrofit you have to run them hotter than ideal to get enough heat output from small radiators, in that case you either live with just getting 85% or change to larger or finned radiators. In any case a modern gas boiler should take 35% or so off your gas bill at moderate cost.
Or a heat pump as others have discussed, subject to your electricity not being more than about 3x the cost per unit* than gas.
*Convert to the same unit, Joules, kWh, whatever. US gas is sold in therms right?
Even with the outdoor fan shut off, air conditioning when it is 30F outside is ferociously efficient and it is really noticeable.
With a hydronic system with a buffer tank it will have less impact, 100L can source a lot of heat.
It's still expensive if you have large storage. I for example have a 1200 liter buffer tank. No antifreeze for me.
In really cold climates a split air to water heat pump might be better, they use a refrigerant loop to the outside unit and put the water unit inside. No need to worry about the effects of freezing near the periphery at least.
In really cold climates a split air to water heat pump might be better, they use a refrigerant loop to the outside unit and put the water unit inside. No need to worry about the effects of freezing near the periphery at least.
I have a monoblock type and don't have the slightest fear about it freezing. It seems the natural convection keeps the water running within the unit even if water pump fails or power goes out, I have tested this; this happens as long as there is some height difference between the buffer tank and the heatpump, no super long horizontal piping, and no unnecessary check valves (because the natural convection seems to start the opposite way). Besides, I have insulated the pipework almost excessively well, also added some extra insulation inside the heat pump, although the Chinese did quite acceptable job with Armaflex.
With long-term power outage, it would take ages for that 1200liter buffer tank to start freeze, and when it comes to that, it's game over anyway unless I'm physically present either burning some wood, or bleeding water off everything.
With a hydronic system with a buffer tank it will have less impact, 100L can source a lot of heat.
Hydronic systems are rare in this part of the world, at least 95% of houses in my region have some form of forced air heating system. Most of what remains are older places with electric resistance baseboard heaters. I have only ever seen 2 or 3 houses around here with hydronic heat, I think it's a lot more common on the east coast.
*Convert to the same unit, Joules, kWh, whatever. US gas is sold in therms right?
Yes. 1 therm is 100,000 BTU/h.
Last time I did the math, my electricity was almost 3 times the price of natural gas, so heat pump vs natural gas was pretty much a wash. I hear natural gas is supposed to increase sharply in price at some point so that might change, but then around 15% of our electricity in this region comes from burning natural gas so I expect that to go up too.
Modern air source heatpumps, those that are actually designed for heating around or below freezing point, for some last 10 years, have improved defrosting quite a bit.
It's mostly a software thing.
Modern high efficiency systems are much better, however they have only recently started to gain some traction. The vast majority of installed heat pumps are still conventional units that have no software at all, the only electronics in the unit is the defrost timer which at least in a lot of them is just discrete logic.
I helped a friend install a Mitsubishi mini split back in the spring and that was a huge improvement but those are still expensive, especially in the larger sizes that can heat a whole house.
OP - For heat loss, get a thermal imaging camera and evaluate the house. Even if you have to rent one, totally worth it and you can split costs with a neighbor if you do their home as well. Worst offenders are entrance doors (weatherstripping), windows (damaged seals) and shoddily installed insulation, and air leaks from sloppy carpentry.
High efficiency boilers are a money loser on maintenance. They have more sensors, more relays, more combustion chamber corrosion (acidic condensate), complicated expensive control board, plastic piping etc. which means they have a short life and you will spend more on repairs which can scuttle your savings. Condensing boilers were apparently mandated in the UK 2005 and may not have lived up to the marketing hype. Pre-check
US recalls so you don't get sold an old lemon.
I have Grundfos pumps with built-in VFD in constant pressure-differential mode, it throttles the pump based on demand. This does save some electricity compared to the prior Bell&Gossett always running in spring/fall when there is no demand for heat, it's a small waste.
You'd likely have to upgrade combustion air supply - this is constant cold air coming in and making the basement cold, unless you get a damper and actuator.
For the Net-Zero homes, of all things a fireplace proved to be invaluable. Whether you're burning a lump of coal or wood, great in a zombie apocalypse to keep the house livable and augment heating. One guy I know uses coal in it all winter to save money on heating, although neighbors complain about the stink.
I installed a condensing furnace 16 years ago and in that time it has never had a problem. I don't know why anyone would even consider an old low efficiency furnace or boiler, there's no way it will work out cheaper over time. I've heard people say the high efficiency stuff is failure prone but I haven't seen it. Modern electronics are pretty reliable and most of this stuff has around a 20 year warranty on the heat exchanger. What is the problem with plastic piping? I have replaced galvanized pipes that were clogged with mineral growths, and I've replaced galvanized B-vent flue pipes that rotted out, but I have never had to replace a plastic pipe. This sounds like the arguments I was hearing 16 years ago which have turned out to be completely baseless.
OP - For heat loss, get a thermal imaging camera and evaluate the house. Even if you have to rent one, totally worth it and you can split costs with a neighbor if you do their home as well. Worst offenders are entrance doors (weatherstripping), windows (damaged seals) and shoddily installed insulation, and air leaks from sloppy carpentry.
This is a great suggestion, I borrowed a camera from work to do my house.
High efficiency boilers are a money loser on maintenance. They have more sensors, more relays, more combustion chamber corrosion (acidic condensate), complicated expensive control board, plastic piping etc. which means they have a short life and you will spend more on repairs which can scuttle your savings. Condensing boilers were apparently mandated in the UK 2005 and may not have lived up to the marketing hype.
The corrosive condensate and thinner heat exchangers can be an issue, though the biggest problem in the UK seems to be badly installed condensate drains that run outside with shallow slopes and freeze up. What we
have had in the UK is a mass switchover to combi boilers, which are multi-function doing both wet central heating and instant water heating (to the point where the general public think a condensing boiler and a combi boiler are the same thing). These have a lot more internal complexity and often barely make it out of their 5-7 year warranty period. This may in hindsight turn out to be a mistake as it means people have spent the last decade removing stored hot water systems that are generally more suitable for heat pumps.
You'd likely have to upgrade combustion air supply - this is constant cold air coming in and making the basement cold, unless you get a damper and actuator.
Surely any new boiler would have a balanced flue? I'm pretty sure that's all we install here now, cold air is drawn from outside into the combustion chamber from an orifice co-located with the exhaust so as to ensure the same pressure despite wind, etc.
As I happen to have the manual open for another reason, here's a typical 10-15 year old UK-style condensing boiler. This particular one doesn't seem to have ever given trouble and is 90% efficient.
https://www.freeboilermanuals.com/assets/pdf/potterton/Potterton_Gold_H_Install.pdf
Surely any new boiler would have a balanced flue? I'm pretty sure that's all we install here now, cold air is drawn from outside into the combustion chamber from an orifice co-located with the exhaust so as to ensure the same pressure despite wind, etc.
In North America they call it "direct vent", there is an intake air pipe and a flue pipe in parallel, or occasionally coaxial. I haven't seen a condensing appliance that didn't support direct vent in well over a decade. In some cases it is permissible to configure them to draw room air for combustion but I can't think of many reasons to do that. Certainly if your furnace/boiler is located in conditioned space you would always want to use direct vent.