The humble water heater could be the savior of our energy infrastructure woes • Hacker News Board

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

#211

Post by devwastaken » Wed, Jul 07, 2021, 3:50 PM UTC

dvdkhlng wrote: post #119

devwastaken wrote: post #106

Earlier quoted context omitted.

Tankless are also useless if you don't have perfect water, and even if you do you have to descale them every year. The calcium, iron, and others in your water builds up in the small copper pipes, and an acidic cleaner is required to remove it. If youve ever used a Keurig it's similar. Propane water tanks are pretty bulletproof. Even with bad water they just truck, and require no electricity to operate, unlike some ot…

Where I live, tankless heaters are pretty wide-spread. They connect to 3-phase power supply, heating at a variable power level up to 24 kW [1]. They need almost no maintenance, nobody I know has ever descaled one. I think the better units directly run the heating wires through the water, so they do not calcify due to small surface area (or maybe the huge temperature gradient when operated breaks the calcification lay…

Is that on well water or city water? In the country in the U.S. every body has individual wells, which comes with a lot of iron and calcium.

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

#212

Post by opwieurposiu » Wed, Jul 07, 2021, 3:51 PM UTC

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.

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.

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

#213

Post by WJW » Wed, Jul 07, 2021, 4:02 PM UTC

korethr wrote: post #130

adrianN wrote: post #81

Earlier quoted context omitted.

If you use the electricity to run a heat pump you can get a couple more Joules out of the gas. Ideally your gas-plant is also connected to a district heating network, so the 60% heat are not completely lost.

A thought occurs to me just now: Why not also use that 40-60% waste heat to drive district cooling during the hot season? There's the absorption refrigeration cycle[1], which requires only a a heat input to drive the cycle to pump heat from the cold side to the hot side. Is the difference between the coefficient of performance between the more common vapor-compression cycle and the absorption cycle such that it is mo…

Both cycles are limited by the same fundamental value (the Carnot coefficient) so I don't think that it would be a huge difference between the two cycles. Rather, I suspect that there are not all that municipalities that have (or need) both district heating AND district cooling. I expect that in the future we'll see a lot more industrial use of waste heat from power plants though, and part of that might take the form of on-site absorption chillers.

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

#214

Post by jojohohanon » Wed, Jul 07, 2021, 4:03 PM UTC

opwieurposiu wrote: post #212

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. The water will get up to 80c on a sunny day, s…

When hooked up to the grid, converting from electricity to heat for storage makes alot of sense (to me).

But I'm curious about your case: why not use the old-fashioned solar water panels to create hot water directly?

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

#215

Post by sidewndr46 » Wed, Jul 07, 2021, 4:22 PM UTC

scotty79 wrote: post #201

sidewndr46 wrote: post #182

Earlier quoted context omitted.

Is English a second language for you? I ask not because I am trying to insult, but what you are describing is just called geothermal heat in North America. It can also work in reverse if the air temperature is higher than the ground temperature. Also, you have your units wrong. Electrical demand is measured in just kilowatts (kw). Actual usage is in kilowatts-hours (kwh) which is just an unusual way of saying joules.

Units are fine. He just said he gets energy as heat in the amount 4 times higher than amount of electrical energy he uses to get it. It's fine to talk about it in terms of energy as it would be to talk about it in terms of power. And I'd argue that kWh is exactly the usual way of saying 3600000 joules. Also name "geothermal heat" for ground heat pumps might be a local US marketing term. In international English geoth…

I don't know anything about Iceland but I am using the definition from energy.gov

https://www.energy.gov/energysaver/heat-and-cool/heat-pump-s...

Geothermal works with either vertical holes in the ground or a big loop spread out horizontally. Neither one is very deep nor does it involve hot rocks.

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

#216

Post by BizarroLand » Wed, Jul 07, 2021, 4:48 PM UTC

mabbo wrote: post #202

plater wrote: post #189

Earlier quoted context omitted.

Not sure what a cold basement has to do with it? You suck in air from outside, extract the energy, and blow out colder air. The warm water is stored in an isolated tank (sure if the basement is cold it might cool off slightly quicker, but you warm up the cold basement which is a good thing). It is then used for heating the house via radiators as well as for warm tap/shower water. We use it to warm a 240m2 house with…

The problem is in "extract the energy". If your refrigerant can reach -20 in your system, and it's 30C outside, then your refrigerant is exchanging 50C of energy per cycle. But if it's -15C outside, the best you can achieve is 5C of energy exchanged per cycle. And at -20C outside, you can't exchange heat at all. That's a bit hand-wavey and not exact units, but I think it accurately describes the problem. What the abo…

That is why they are hybrid heat pump water heaters. When the air is insufficiently warm to heat your water, the heat pump can switch back to traditional electric heater rods.

They do run about 2x the price of a non-hybrid (My local hardware store has an 80 gallon hybrid for $2250 vs $1080 for the non-hybrid) but my power company is offering a $500 instant rebate as well as the county offering a $300 rebate, so in my case, it's a few hundred extra bucks for a few hundred dollar annual reduction in my power bill.

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

#217

Post by BizarroLand » Wed, Jul 07, 2021, 4:54 PM UTC

brtkdotse wrote: post #132

kpozin wrote: post #126

Earlier quoted context omitted.

Out of curiosity, what is the effect of this thick insulation on indoor CO₂ levels? Do these houses usually have ventilation systems that can compensate?

Usually heat exchanger ventilations. Fresh air comes in and exchanges heat with used air coming out, so you get fresh air but with the indoor temperature.

HRV (Heat Recovery Ventilator) systems are really cool, too. They solve the ages old problem of bringing fresh air into a home without losing all of the temperature and humidity from the internal environment.

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

#218

Post by BizarroLand » Wed, Jul 07, 2021, 4:57 PM UTC

elric wrote: post #193

manmal wrote: post #74

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.

That many cars seem undesirable in urban areas (or anywhere, really, but let's not go there). From a bit of quick searching, EV battery packs are roughly the same volume as a fridge, and weigh in around 300kg (that was a Nissan Leaf specifically, but I assume others are similar). I don't have enough room for a fridge sized battery in my house. It'd be nice if they could shrink a bit. With enough capacity to run a tan…

On the other hand, if every home had a load leveling battery system of even modest storage capacity, say, 15 minutes average power usage covered, then load leveling would not be nearly the problem it is today.

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

#219

Post by giantg2 » Wed, Jul 07, 2021, 5:14 PM UTC

BizarroLand wrote: post #216

mabbo wrote: post #202

Earlier quoted context omitted.

The problem is in "extract the energy". If your refrigerant can reach -20 in your system, and it's 30C outside, then your refrigerant is exchanging 50C of energy per cycle. But if it's -15C outside, the best you can achieve is 5C of energy exchanged per cycle. And at -20C outside, you can't exchange heat at all. That's a bit hand-wavey and not exact units, but I think it accurately describes the problem. What the abo…

That is why they are hybrid heat pump water heaters. When the air is insufficiently warm to heat your water, the heat pump can switch back to traditional electric heater rods. They do run about 2x the price of a non-hybrid (My local hardware store has an 80 gallon hybrid for $2250 vs $1080 for the non-hybrid) but my power company is offering a $500 instant rebate as well as the county offering a $300 rebate, so in my…

Wow 80 gallons is huge. I can see it making sense at that volume.

I find the benefits to be marginal when using an average 40 gallon or less and only using it for 1-2 people. The use of water conserving fixtures further reduces the benefits for smaller tanks with fewer people (not sure they even make them smaller than 40 with the heat pump). With the exception being for people in hot climates with the tank in the garage or similar space.

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

#220

Post by kragen » Wed, Jul 07, 2021, 5:47 PM UTC

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'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't require a temperature-limiting valve to keep you from scalding yourself.

However, even if hot-water heaters aren't where it'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'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 https://news.ycombinator.com/item?id=27757018 allow an order of magnitude higher energy storage density and easier temperature control, and "thermochemical energy storage" (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.

I wrote extensive notes on this in https://dercuano.github.io/topics/thermodynamics.html (especially https://dercuano.github.io/notes/big-if-true.html#addtoc_8 and https://dercuano.github.io/notes/household-thermal-stores.ht...) and also Derctuo and Dernocua.