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

#201

Post by scotty79 » Wed, Jul 07, 2021, 2:22 PM UTC

sidewndr46 wrote: post #182

jcynix wrote: post #97

Earlier quoted context omitted.

Good heat pumps aren't of the air conditioner type. Our heat pump uses two 60m deep drilled holes. Thus heat exchange happens in the ground, which is always more or less 10 degrees Celsuis. Heat exchange in the house happens through floor heating. So during a hit summer, the reverse capability just pumps the cold water through our floors (controlled for the dew point) and the warm floor water into the ground. That, c…

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 geothermal means rather what Iceland is mostly doing. Pumping water into very hot rocks deep below to extract heat. And it doesn't work in reverse because it would be additional work to pump heat into very hot rocks instead of dumping it into the air or into the cool ground 2 meters below the surface.

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

#202

Post by mabbo » Wed, Jul 07, 2021, 2:23 PM UTC

plater wrote: post #189

giantg2 wrote: post #184

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't there given the low cost of electricity, which green energy will continue to drive down. I don't…

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 above poster is saying is that as temperatures drop, the system gets less and less efficient. For some environments, it may become cheaper to use resistive electric instead.

The 'Technology Connections' channel did a series of videos about heat pumps that are fascinating and I highly recommend: https://www.youtube.com/channel/UCy0tKL1T7wFoYcxCe0xjN6Q.

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

#203

Post by scotty79 » Wed, Jul 07, 2021, 2:24 PM UTC

PeterisP wrote: post #153

elric wrote: post #104

Earlier quoted context omitted.

> Good heat pumps aren't of the air conditioner type. Our heat pump uses two 60m deep drilled holes. Thus heat exchange happens in the ground, which is always more or less 10 degrees Celsuis. Good point. The source and destination of heat can be air, water, or "ground source". But it's still all just the same concept as A/C units. Pump heat to one place, using less energy than what it would take to heat it using resi…

The special thing about ground source heat pumps is, well, that they use ground instead of air - and it turns out to be a really important thing because of the temperature differences between ground and air. A/C or heat pump efficiency is directly related to the temperature difference over which you're trying to pump. If the temperature difference is twice as large, you need to spend twice as much energy to pump the…

However there are air heat pumps which differ from the AC ran in reverse only in how the heat is distributed around the house. For example with warm water in the pipes not just blowing warm air around.

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

#204

Post by landemva » Wed, Jul 07, 2021, 2:25 PM UTC

matheusmoreira wrote: post #173

cycomanic wrote: post #88

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. 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 co…

Is it possible to hook up computer heat sinks to these things? I figure it'd be better to pump the heat outside my home instead of dissipating it into my air conditioned rooms...

I want that for my fridge. Move the compressor and radiator somewhere else than the kitchen.

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

#205

Post by scotty79 » Wed, Jul 07, 2021, 2:36 PM UTC

simlan wrote: post #105

tacLog wrote: post #103

Earlier quoted context omitted.

Is it though? It might be cheaper in many area's but this source [1] says that the grid transmission loss is only 5%. Am I missing something that makes it a more substantial difference? Not to mention that piping all that natural gas out to each home has to result in a certain amount of leakage and energy cost in just the pumping itself. [1] https://www.eia.gov/tools/faqs/faq.php?id=105&t=3#:~:text=Th... .

Gas to electricity efficiency is low so you loose more then half the energy when producing electricity from gas. Using a 90 percent efficiency furnace to heat water directly with gas is the better solution. Assuming your electricity comes from gas plants.

However if you heat with heat pump you are getting more than 3 times more heat than electrical energy you used. So despite getting only 0.5 energy by turning gas into electriciy you are getting 3*0.5 = 1.5 of heating and you could go in reverse and get the cooling when you need it.

If you have a gas line to your home the most efficient way of heating would be to have co-generation gas turbine than makes heat and electricity and then use the electricity produced to power heat pump.

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

#206

Post by bluGill » Wed, Jul 07, 2021, 2:45 PM UTC

brtkdotse wrote: post #186

bluGill wrote: post #165

Earlier quoted context omitted.

If you are only worried about natural cooling, insulation is not the answer. You want a poor insulated house with a lot of shade, and large open windows for the wind to blow through. Most people these days want more than natural cooling. As soon as you decide to have an AC system installed more insulation is better for the reasons you state.

No. You never want poor insulation. Poor insulation means that the indoor temperature will always match outdoor temperature. There's not such thing as "natural cooling", only thermodynamics.

Natural cooling is about sweat (water evaporation), and staying in the shade. Lots of wind helps.

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

#207

Post by gdubs » Wed, Jul 07, 2021, 2:57 PM UTC

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?

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

#208

Post by philote » Wed, Jul 07, 2021, 3:05 PM UTC

mabbo wrote: post #198

elil17 wrote: post #45

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. Unfortunatel…

You'd like what we have in Toronto- we use Lake Ontario as a heat sink. https://en.wikipedia.org/wiki/Enwave#Deep_Lake_Water_Cooling... 75% less energy than traditional air conditioning.

Doesn't that increase the lake's overall temp though?

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

#209

Post by opwieurposiu » Wed, Jul 07, 2021, 3:31 PM UTC

gdubs wrote: post #207

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 used to work at place that installed this exact system. You can get an extra 2-3 months a year use of your pool in warm climates. It does work but we sold way more geothermal systems then these pool based systems.

Issues: Building inspectors do not like it because it is non-standard. Copper is attacked by wet chlorine so you have to use stainless heat exchangers and plastic pipe. Pool filter must be constantly maintained to ensure the AC does not get clogged. If the pool is small, it can become very warm in august, almost like a hot tub.

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

#210

Post by mabbo » Wed, Jul 07, 2021, 3:39 PM UTC

philote wrote: post #208

mabbo wrote: post #198

Earlier quoted context omitted.

You'd like what we have in Toronto- we use Lake Ontario as a heat sink. https://en.wikipedia.org/wiki/Enwave#Deep_Lake_Water_Cooling... 75% less energy than traditional air conditioning.

Doesn't that increase the lake's overall temp though?

Probably not, because there's a second interesting fact about the system (which I just learned): the water isn't returned to the lake directly.

Instead it's used as an input to the filtration plants, cleaned, and used as municipal water. I'm not sure what the overall effect of getting slightly warmer water in the municipal system is, but I bet it's a win overall since we spend so much energy heating up water (as per the article!).

Edit: also the lake is 1600 cubic km of water, so I dunno if we could ever noticeably change the lake temperature this way.