The humble water heater could be the savior of our energy infrastructure woes

Another type for thermal battery: ice thermal storage. Instead of running AC, it’s a freezer that makes ice during the night (using off-peak electricity and taking advantage of the cooler nighttime air) and then melts it during the day to cool large buildings. They’re a ridiculously good idea if you’re running a large enough HVAC system - they can even lower capital costs compared to traditional systems. Unfortunately, many building operators don’t use them because they’re unfamiliar with the technology or because they take up more building footprint. <a href="https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Ice_storage_air_conditioning" rel="nofollow">https:&#x2F;&#x2F;en.m.wikipedia.org&#x2F;wiki&#x2F;Ice_storage_air_conditioning</a>

Am I the only one that find this article incredibly confusing?<p>It starts off talking about wanting to move energy production to renewable sources. Great, I&#x27;m with you so far. A major issue with renewable energy (solar and wind) is that they&#x27;re variable, not constant. This results in uneven power. The wind doesn&#x27;t blow, it&#x27;s cloudy or it&#x27;s night time. So we need a way to convert this variable renewable energy into constant energy that&#x27;s accessible around the clock. An obvious solution to the problem is to convert the renewable energy into stored potential energy. This is what pumped hydroelectric dams are all about. Use the variable energy to pump a bunch of water up behind a dam, then release it when you need a more constant supply of energy.<p>Great, so we&#x27;ve got that much figured out. The world needs a way to convert renewable energy into constant energy.<p>And the solution to this problem is... the distribution of more efficient water heaters.<p><i>Wat</i><p>How do more efficient water heaters in any way, shape or form help solve the renewable variable rate energy to constant energy problem? I feel like I must be missing something obvious. Are we able to somehow store energy in heat-pump based water heaters and then extract that energy to run other items in our homes? When you store energy in a heat-pump based water heater does it not need to run at night when renewable energy sources are lowest?<p>Can anyone explain to me what the heck this article is talking about?<p>I feel like I&#x27;m missing the larger picture, but I don&#x27;t see how these two concepts (energy storage and appliance efficiency) are related.

In Northern Europe heat pumps are now pretty much standard for new homes. They reduce heating bills quite dramatically compared to other technology. In particular if combined with solar power.<p>One big advantage is that they can also be run in reverse so you could cool the house in summer (although you might need a special heat pump to do this, especially to separate from the hot water). In areas where it gets very cool, one can also use connect the heat pump to the ground as heat sink which improves efficiency even more.

This is old technology, I&#x27;m surprised the US hasn&#x27;t already implemented it.<p>They have been remote-controlling water heaters in New Zealand and Australia since the 50s. Just a simple relay installed in each house that responses to extra frequencies on the power lines in the 160-1600hz range. It&#x27;s called ripple control, for obvious reasons. Each home gets assigned to one of several channels in each area so they can have more fine grained control of the load.

I have a tankless hot water heater system in my new home that runs on a city natural gas line. It’s super efficient and thus my energy bills are very low compared to what I used to pay for the traditional electric hot water heater in my previous home, however it’s not a silver bullet. I find myself running the water for a ridiculously long time in order for the water to start getting hot, sometimes for more than a minute, depending on where I am in the house (obviously the farther you are from the heating unit, the more time it takes for the hot water to travel to its destination). Our water consumption is therefore quite a bit higher, thus I am not confident this is a good ecological or financial tradeoff. I have used similar systems in Europe and they seem to be a little quicker, but that could be from higher water pressure. They seem to suffer from the same problem though. Perhaps a good solution would be to have a small (4-5 gallon) booster tank that is periodically heated like a traditional tank-based system, so that when hot water is run, it can immediately be delivered while simultaneously engaging the on-demand system. Forgive my layman’s terminology, I’m not a plumber or HVAC engineer, but hopefully the idea is clear.

&gt; One flashy idea for storing energy goes something like this: dam a river,<p>Incorrect. Or rather not necessarily correct. Pumped hydro does not necessarily require damning a river.<p>&gt; Making matters worse, about a quarter of the energy is cannibalized to do all that pumping.<p>Pumped hydro is largely considered one of the most efficient forms of energy storage, beating most other methods by a fair amount.<p>&gt; This approach can be deployed far faster than dam construction, and free of protest (except perhaps from dam builders).<p>We can&#x27;t do both?

I looked at heat pump water heaters several years ago. They are massively expensive, have a little more risk of failure (potential for expensive repairs), and in many cases would only work for half of the year (basements are a common location and get relatively cold in the winter). I like the idea, the the ROI just wasn&#x27;t there given the low cost of electricity, which green energy will continue to drive down.<p>I don&#x27;t like the idea of the grid or cloud controlling appliances in my home. If I could program the run options myself based on the power company&#x27;s recommendation (like a programmable therostat), that would be better in my opinion.

<a href="https:&#x2F;&#x2F;archive.is&#x2F;NrQQC" rel="nofollow">https:&#x2F;&#x2F;archive.is&#x2F;NrQQC</a> for those who don&#x27;t want to support Salon with clicks.<p>The article just wanders aimlessly between lies.<p>Pumped Hydro dams are tiny compared to hydro-power or water dams and are beautiful, the same size as solar or wheat farms. A cool seawater based one in Japan - <a href="https:&#x2F;&#x2F;www.google.com&#x2F;search?q=okinawa+pumped+storage+&amp;tbm=isch&amp;oq=okinawa+pumped+storage+&amp;sclient=img" rel="nofollow">https:&#x2F;&#x2F;www.google.com&#x2F;search?q=okinawa+pumped+storage+&amp;tbm=...</a><p>A good example of a government doing something that worked is the Australian government which wanted to spend money fighting the global financial crisis so insulated homes. Unfortunately deaths from the scheme, which were at the same rate as normal but became larger in number stop people talking about it much.<p>This tale of heat pump water heaters stopping a dam is rubbish. Where is the mathematics?<p>Heat pumps are awesome however, go to Technology Connections, not this to learn about them - <a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=7J52mDjZzto" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=7J52mDjZzto</a>

This article contains two suggestions:<p>1. heat pumps rather than resistance heating: move the heat where you want it instead of creating it from scratch.<p>2. timeshifting electrical load. Figure out how to add and shed it on demand.<p>The second one has a remarkable property. Load can be shed much more quickly than spinning up peak-load generators. That means grid operators can, in periods of overload, keep the grid&#x27;s AC frequency (50 or 60Hz) from dropping. Without load shedding it&#x27;s done with expensive and dirty peak-load generators. That&#x27;s called &quot;frequency control ancillary services&quot; (FC&#x2F;AS) in the grid biz, and it&#x27;s economically important: regional grids don&#x27;t work properly unless their local grids all run at the same frequency. Local grids don&#x27;t want to be disconnected from regional grids in peak-load times because their generators slowed from 60Hz to 59.8Hz. Remotely switching off a mess of hot water heaters is a GREAT way to change the grid load quickly if that starts to happen.<p>FC&#x2F;AS is a major driver of the big Australian battery projects (built with parts from Tesla). <a href="https:&#x2F;&#x2F;www.greentechmedia.com&#x2F;articles&#x2F;read&#x2F;australia-picks-massive-tesla-battery-to-ease-transmission-constraint" rel="nofollow">https:&#x2F;&#x2F;www.greentechmedia.com&#x2F;articles&#x2F;read&#x2F;australia-picks...</a><p>Who is the Van Jacobson (TCP designer who dreamed up slow-start &#x2F; exponential backoff) of smart grids? Is it somebody reading HN?

Virtual battery, there is an interesting project to do a similar thing with aluminum smelters where you heat them and operate at full capacity off-peak and then during peak electricity usage you run slower. Since a smelter consumes so much power this can significantly level the grid usage.

Can you also store cold cheaply? For example, to run an A&#x2F;C early in the morning, and put the cold in an insulated tank of a room-temperature phase change material [0]?<p>[0] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Phase-change_material#Common_PCMs" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Phase-change_material#Common_P...</a>

Most newly built electric cars have a 50+ kWh battery. Imagine if smart meters could use _that_, regardless of where the car is currently parked and plugged in. 50kWh is in excess of what most households use in electricity on most days.

Lots of good discussions about water heating in this thread. But it&#x27;s such a tricky topic.<p>Tankless water heaters are pretty efficient, but when you need hot water, you briefly use huge amounts of energy. It&#x27;s for this reason that they almost always use natural gas. Electric tankless heaters are a great way to cause brownouts. They&#x27;re roughly the size of a microwave oven, so they can fit in pretty much any kind of dwelling.<p>Water heaters with tanks, on the other hand, take up huge amounts of space and require frequent (but lower) energy input. This can use heat from a variety of sources, including low quality&#x2F;unrealiable heat sources like solar heat pipes.<p>Then there&#x27;s space heating. Unless you live in a Passivhaus, keeping a comfortable indoor temperature is challenging. Central heating using hot water and radiators is the most common approach where I live. But this again relies on burning hydrocarbons. Or, increasingly, on heat pumps, which require a lot of space, are noisy, and drop in efficiency as the temperature drops.<p>As far as I can tell, there are no silver bullets in either space heating or water heating. If you have a really big house, a big tank is probably a good solution for hot water. But living in a really big house is horribly inefficient in its own way. So I&#x27;m guessing that&#x27;s not the greener approach. Living in a smaller dwelling is more efficient. But it seems there are basically zero good ways to heat small living spaces and hot water for a family of 1-2 living in small houses.

I&#x27;ve proposed this (water heater as battery) innumerable times here on HN. Glad to see it finally catching on!<p>You can do the same thing with the HVAC system. For example, when the sun is high and electricity is cheap, have the A&#x2F;C cooling a large mass of stone or concrete. Then, blow air over it at night to keep the house cool.

Solar hot water heaters are cheap and can easily be 50% efficient, beating the heck out of 21%-efficient mass-market PV cells, often even if the PV cells are driving a heat pump. Thermosiphon-type solar hot-water heaters don&#x27;t even need a pump, just a super-low-pressure check valve. Less efficient, but maybe even better, are safer passively-cooled solar hot water heaters, which can be made out of cheap materials like plastics and cement instead of stainless steel, and don&#x27;t require a temperature-limiting valve to keep you from scalding yourself.<p>However, even if hot-water heaters aren&#x27;t where it&#x27;s at, I think circadian thermal energy storage is a pretty big deal for demand response, and demand response is pretty important for the renewables transition—though not as essential as many claim. There&#x27;s thermal-mass energy storage like the hot-water heater approach (and Trombe walls, and earth-berm walls, and several other possibilities), but phase-change storage like the ice-battery approach mentioned in <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27757018" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=27757018</a> allow an order of magnitude higher energy storage density and easier temperature control, and &quot;thermochemical energy storage&quot; (generally through reversible hydration of desiccants such as CaCl₂) potentially allows another order of magnitude density improvement over phase-change materials, as well as offering the possibility of thermally-driven air conditioning, humidification, and dehumidification, as well as greater controllability.<p>I wrote extensive notes on this in <a href="https:&#x2F;&#x2F;dercuano.github.io&#x2F;topics&#x2F;thermodynamics.html" rel="nofollow">https:&#x2F;&#x2F;dercuano.github.io&#x2F;topics&#x2F;thermodynamics.html</a> (especially <a href="https:&#x2F;&#x2F;dercuano.github.io&#x2F;notes&#x2F;big-if-true.html#addtoc_8" rel="nofollow">https:&#x2F;&#x2F;dercuano.github.io&#x2F;notes&#x2F;big-if-true.html#addtoc_8</a> and <a href="https:&#x2F;&#x2F;dercuano.github.io&#x2F;notes&#x2F;household-thermal-stores.html" rel="nofollow">https:&#x2F;&#x2F;dercuano.github.io&#x2F;notes&#x2F;household-thermal-stores.ht...</a>) and also Derctuo and Dernocua.

I have 1200w of solar panels hooked directly to the lower element of my hot water heater. I sized the element to match the source impedance of the panels in full sun. If you use a MPPT system you could get 50% more power in partial shade but panels were so cheap it was not worth the complexity. The top heating element is still on city power as backup but I rarely use it.<p>The water will get up to 80c on a sunny day, so it can store enough heat to last a couple days without sun. There is a mixing valve so the water coming out of the tank is mixed with cold to stay below 50C for safety.

I think these water heaters in question are actually hybrid units. They cool the surrounding room to maintain a temperature set point. In some places, colder room air and thus more condensation is not appreciated.<p>A less-sophisticated approach is to put your tank heater on a timer. Think carefully before you do this. Does your tank heater have the capacity to keep the water hot for a full shower, until you’re back under the non-peak schedule? If it doesn’t, you’ll be the first to hear about it.

I’m not sure if this is a stupid idea, but I think of all the energy people spend in places like LA to heat their pools even in the very warm months, while blasting AC inside. This seems like a pretty good opportunity for using a heat pump to take the cold pool water and use that as a heat sink for the hot indoor air. Or is there something about this setup I’m missing?

<i>bangs head on table</i><p>Energy efficiency&#x2F;load redirection is not the same as energy storage.<p>Heat pumps water heaters, with good insulation is about 3-3.8 times more efficient than straight electric heating. However keeping hot water hanging around isn&#x27;t all that efficient.

Meanwhile the EU is intending to ban hot water tanks in favour of instantaneous heaters.

I&#x27;m able to turn my water heater off twice a week without a noticable difference in the water temperature. I wish there was an easier way other than flipping the circuit breaker.

That kind of thing is chronically overestimated. Amory Lovins does for that what the 1960s boosters of nuclear power did for the LWR.<p>So much in the energy field is like a stopped clock.

&quot;This approach can be deployed far faster than dam construction&quot;<p>Can we really manufacturer that many hot water tanks in less time than building a damn?

What the enthusiasts for heap pump water heaters miss is the source of the heat they are pumping.<p>In the summer they are removing heat from a hot house, great - free air conditioning.<p>In the winter they are removing heat from a warm house, which then needs to be replaced by some other heating source to keep the house warm, great - you get to pay twice.<p>I tried turning the heat pump element on my heater off during the winter. However, it is programmed to automatically turn on again after 5 days.