[Technology Connections] My water heater is cooler than yours
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My water heater is cooler than yours
Cooly hot. Or hotly cool.Follow-up video:https://youtu.be/fHPCS8j3cRMOther stuff:Technology Connections on Bluesky:https://bsky.app/profile/techconnectify.bs...
I picture a world where everything in the house runs off a single heat pump, and heat gets diverted from your A/C into your water heater and clothes dryer.
I assume the difficulty is the refrigerant plumbing? And integrating between different systems?
I mean you’d have to basically build the whole house around it. And I’m not sure about the feasibility of moving heat around to more than 2 devices…
Central heating systems use recirculating hot water to spread meat from a central heater (which can be a heat pump) to multiple radiators. In theory there’s nothing preventing you from connecting other devices to that loop of recirculating hot water to use the heat from your central heating system for those too.
It would however add quite a bit of complexity to the devices and plumbing, which would also make both more expensive.
And it also wouldn’t really be worth it. Heat pumps get less efficient when the temperature difference between the hot and cold side gets larger. So while your air conditioning does indeed produce heat, dumping that heat into the outside air at ambient temperature is much more efficient (in terms of watts of heat moved per watt of electricity used) than trying to use it to heat up water to 50° or so to be used as heat source for a dryer. Then there’s also the issue of balancing demand and supply of heat. Your dryer could only use excess heat from your air conditioning if both are running at the same time, so the devices need to be synchronised or you’d need heat storage, which adds additional complexity, expense and inefficiencies.
Devices that need heat also do not all need the same temperature. Your radiators, clothes dryer, dishwasher and so on all have different ideal temperatures, and because heating pump efficiency decreases as the temperature difference between the hot and cold sides increases it’s more efficient to run it with the lowest temperature delta that’s feasible. So it’s more efficient to just give each device that needs either heating or cooling its own heat pump (unless you have sets of identical devices which all need the same temperature and that can all be integrated in a single system, such as central heating radiators or floor heating zones). And the complexity involved in distributing heat between unrelated devices in your house makes giving them all their own heat pump likely the cheaper option too.
Systems that circulate ' freon' are fairly common in commercial buildings. They are complex to build and so don't really make sense for houses.
It’s possible to heat things like return water or cold water directly and then use heat exchangers.
Temperature differentials also doesn’t matter much because temperature doesn’t directly behave like voltage, if your hot source is too hot you simply use less hot water (lower flow). You’d likely end up with multiple heat pumps throughout a larger home, but each one can be smaller as they cooperate.
Here in Sweden we already always distribute to homes at 70-100°C and then at 50-55°C internally (again, with heat exchangers to minimize energy loss). And that works just fine. We just don’t (yet) have many systems which feed back thermal energy.
You can easily feed back to a central hot water tank, then let the central heater rest as another heatpump returns energy to it.
The different temperatures are not a problem because they’re difficult to achieve or anything. Most devices that need heat would have a pretty wide tolerance. The main problem is efficiency, when that heat is provided by a heat pump.
If you have underfloor heating, that can typically work with water temperatures as low as just 30°C. If you have a heat pump that needs to heat up water to 30°C, with outside temperature being at about 0°C (realistic winter temperature here, and it makes the calculation easy), then a good heat pump typically reaches a CoP of 4 (sometimes even slightly more).
If you instead would use an internal heat grid of 65°C (a pretty typical practical maximum of conventional heat pumps, and a pretty typical temperature for a heat pump powered clothes dryer to run at), then that CoP typically drops to only just about 2.
So, if you let your heat pump run at 65°C and use a heat exchanger to run your heating off of it at 30°C, you use nearly twice as much electricity for every watt of heat you add to your house compared to just running the heat pump at 30°C and using the output directly.
Typically the heating in a home is the application that demands the most amount of heat by far. But it’s also the application that is usually the most tolerant to low temperatures (especially if you have underfloor heating or forced airflow radiators). So you save a huge amount of electricity by having the circulating water temperature as low as possible, but that also makes that heat not very useful for most other devices (a clothes dryer operating at only 30°C would be highly ineffective).
Heat grids work great if they are supplied by industrial waste heat. But if the heat has to come from a heat pump they’re a terrible idea because of how much heat pump efficiency decreases with increasing temperature delta.
sidite-solar.com/cold-climate-performance-cop-dat…
You assumed 0°C? They solved it at winter temperatures most of Sweden sees.
Any COP above 1 eventually pays off, as long as it does so before the equipment is due for replacement you’re good.
You clearly did not read the full comment chain, nor my full comment.
Your comment makes the error of assuming “not peak efficiency isn’t good enough” even if a ratio just above 1 pays off if other energy sources are more expensive. Such as when you need more heat than the burned waste can provide. Or when you need to maintain the temperature of the hot water tank after filling it. You just need it to pay off before you need to replace the equipment.
Literally just see the video you responded to - some of these tanks can even maintain a thermal gradient in a single water tank and doesn’t have to heat it all to max at once, and some can even provide water out at multiple temps this way. If you get that kind of machine that delta is irrelevant. And also, as the video shows, the top-up heating efficiency is actually high - when it starts at a high temperature and raises it a few more degrees.
You’re also forgetting the per-machine overhead - a home having multiple heat pumps helps in large buildings, but you do not want one for every tap, etc. You want them where you have large thermal energy flows.
Do you think an installation with a CoP of >1 gives you free energy or something? It does not. An installation with a CoP of 2 still uses energy, and twice as much for the same heat demand as an installation with a CoP of 4. A CoP of 1 would be equivalent to a resistive electric heater, which is generally considered to be the worst way to heat a house. Cost wise with the energy prices in my area you need a CoP of between 2.5 and 3 to break even in energy costs, and with the grid here still being largely dependent on coal and gas in the winter you’d need a CoP of around 2 to be positive in CO2 footprint. Most heat pumps can easily reach that CoP, when used sensibly.
Tanks with thermal gradients also do not matter for CoP. What matters is the difference between the hot side and the cold side. If you have to heat something up to a higher temperature, that efficiency is lost, regardless of what happens with the heat afterwards.
The video also shows the exact opposite of what you claim. You can clearly see that the power required to run the heater goes up as the temperature increases. And yes, topping up requires relatively low amount of power compared to a cold start, but that’s because it doesn’t have to add much heat energy to the tank, not because of a difference in efficiency during top-up.
I’m also not saying you need a heat pump for every single tap, I’m just saying that relying on one single heat pump for all your heating and cooling needs in your house is a stupid idea. It of course makes sense to have one heater for all hot water taps in your house. But it does not make sense to run your heating and dryer on the same heat pump, unless you like wasting a lot of electricity.
You also mentioned per-device inefficiencies, but it’s actually the opposite. Heat pumps are at their most efficient when properly sized for the installation. If you have only a single unit then it has to be sized for the peak demands you might need, and it will not run at peak efficiency in the summer when it just has to power your dryer. Having a dedicated heat pump inside the dryer that is properly sized for exactly the heat output the dryer needs is much more efficient. And that is even ignoring inefficiencies behind heat distribution you’d have with a centralised setup.
We already have hot and cold water distribution. Most Swedish homes have central heating using hot water radiators, and central cooling is now starting to become a thing here. Any sink in a house has hot and cold water.
It’s absolutely possible to tie into this by making use of recirculation systems where you have constant flow of hot/cold water and every household source of heat or AC unit for cooling can tap into it (pun intended) to feed back generated heat or contribute to cooling. Then you use storage systems (thermal mass or thermoelectric generation) for the excess.
Yes but that hot water in your house has to be heated… And if it’s not connected to your AC then there’s no way for the cold being created to get back into your house. It’s just being dumped as waste energy into the atmosphere.
Pun? More like a single entendre…
Well, try storing heat for later use. How do you do this as a temperature battery?
An efficient device like solar panels are still much much less effective without batteries. In the same vein, producing or moving heat right now doesn’t mean some other room or device needs the excess or inverse right now.
Nobody runs a dryer constantly, for example. If there’s barely any heat to pull when it is needed, how do you solve for that? Generating heat goes against the goal of recycling it with a central system.
Most houses have hot water tanks
If you watch the video, you’ll understand that the temperature transfer process to a hot water tank is incredibly slow. So, water tanks are not a very good battery.
I mean, unless you want to spend 12 hours trying to dry your clothes.
But that’s not a technical limit, it’s a cost saving engineering limit
Also you can pull heat out much faster when needed. If there’s heat left when you’re done you can feed it back with a heat exchanger
Interesting problem… how do you store energy when it comes in the form of small heat differentials? That sounds like one hell of an interesting battery.
Maybe if there was also a natural source of cold, as well as a natural source of heat. The problem might then be to store the hot/cold inside a material until they can be mixed. Then mixing in such a way that allows energy extraction?
Except you wouldn’t mix them directly. You’d instead let them try to mix thermally, while forcing the heat to travel through something that allows energy extraction.
en.wikipedia.org/wiki/Ground_source_heat_pump
You can have both!
Also, see reverse flow heat exchangers
Geothermal systems can do that for water heaters, AC, and heat, so… They kinda already do that.
Geothermal doesn’t really work great in many situations for a lot of different reasons. That’s why heat pumps exist.
They might mean ground source heat pumps?
Which situations? This sounds like FUD.
Do you realize that geothermal makes up ~1% of all HVAC systems? So you think 99% of people are just being FUDed?
Solar panels make up ~1% of all residential power generation. I guess that means it’s a horrible way to generate power, right? 🙄
No one said it was “a horrible way to generate power”. I said it “doesn’t work great in many situations”. I don’t appreciate you twisting my words. And yes, that also applies to solar, so thank you for backing up my argument.
If you live somewhere you can’t install it (because you don’t own the building) sure. If you do own the building (or have permission) then it works in pretty much any place you can dig deep enough
You’re the one that equated “unpopularity” with “not a viable solution” with that ~1% response.
Popularity and technical viability have nothing to do with each other. It’s just that the former requires a lot of marketing to push the general public forward, way more than is necessary in my opinion.
You are once again twisting my words, this time even directly misquoting me. I don’t know why. It’s really weird and rude and I’m not going to continue engaging with it.
Better yet a CPU cooler for your PC or game systems.
huh?
Terrible redundancy
I love my hybrid water heater. Having it only kick over to heater when it hits high demand. The fan on the exchange feels amazing during our hot summer months.