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

#181

Post by bserge » Wed, Jul 07, 2021, 1:23 PM UTC

elric wrote: post #92

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…

> One big advantage is that they can also be run in reverse I don't get why this is an advantage. That's just plain old air conditioning, which is genreally considered to be a wasteful, energy guzzling luxury in colder climates. The heat pump hype is a bit puzzling to me. Here's a TreeHugger article which puts it better than I can: https://www.treehugger.com/why-are-there-so-many-fist-pumps-...

Compressors (the biggest power usage in an A/C) have gotten more efficient, plus they remove the fans in favor of dumping heat straight into the ground. That's about it, it's still basically an A/C unit.

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

#182

Post by sidewndr46 » Wed, Jul 07, 2021, 1:23 PM UTC

jcynix wrote: post #97

elric wrote: post #92

Earlier quoted context omitted.

> One big advantage is that they can also be run in reverse I don't get why this is an advantage. That's just plain old air conditioning, which is genreally considered to be a wasteful, energy guzzling luxury in colder climates. The heat pump hype is a bit puzzling to me. Here's a TreeHugger article which puts it better than I can: https://www.treehugger.com/why-are-there-so-many-fist-pumps-...

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.

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

#183

Post by nraynaud » Wed, Jul 07, 2021, 1:31 PM UTC

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…

I'm curious of the mechanics of this, since the expansion of ice makes it a pain to manage.

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

#184

Post by giantg2 » Wed, Jul 07, 2021, 1:37 PM UTC

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 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's recommendation (like a programmable therostat), that would be better in my opinion.

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

#185

Post by Maximus9000 » Wed, Jul 07, 2021, 1:38 PM UTC

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…

If I recall correctly, these are not suitable for residential use, right?

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

#186

Post by brtkdotse » Wed, Jul 07, 2021, 1:40 PM UTC

bluGill wrote: post #165

konschubert wrote: post #149

Earlier quoted context omitted.

As far as I know, Insulation should keep the house cool in summer, because it keeps the heat out. Of course, once the heat is in, you need a way to get it out (at night, through windows). Unlike a greenhouse, insulation is not directional.

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.

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

#187

Post by sidewndr46 » Wed, Jul 07, 2021, 1:40 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…

Combined cycle power plants do use the waste heat:

https://en.wikipedia.org/wiki/Combined_cycle_power_plant

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

#188

Post by brtkdotse » Wed, Jul 07, 2021, 1:42 PM UTC

jcynix wrote: post #145

brtkdotse wrote: post #124

Earlier quoted context omitted.

> Airflow based heat pumps are less efficient, and more noisy outside, of course. This is only true when the ambient temperature dips below the geothermal temperature which depending on your location should make you prefer one over the other.

Germany. Where temperatures dip for some months below the geothermal temperature. Efficiency of air based pumps drops markedly when temperatures reach below 0 degrees Celsius. And last but not least: ground / water carries much more energy per volume unit than air does. So air based heat pumps would make more sense in Europe's south and less sense farther north.

Modern water/air heat pumps have surprsingingly high efficiency down to -20C. We're running a 10 year old model that has no trouble heating our house down to -12, after which a direct electric helper element kicks in.

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

#189

Post by plater » Wed, Jul 07, 2021, 1:47 PM UTC

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 four inhabitants. It works well down to -10 to -15C.

During the night we pay only have the price per kWh to the utility company (as they have excess capacity during that period).

It works great and it pays itself back quite fast.

It's not controlled by any cloud. You can regulate on the control panel how and when you want it to run and it adapts with the weather too if you want.

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

#190

Post by giantg2 » Wed, Jul 07, 2021, 1:48 PM UTC

bluGill wrote: post #165

konschubert wrote: post #149

Earlier quoted context omitted.

As far as I know, Insulation should keep the house cool in summer, because it keeps the heat out. Of course, once the heat is in, you need a way to get it out (at night, through windows). Unlike a greenhouse, insulation is not directional.

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.

It depends on the insulation type. If you're using mass as insulation, it can keep the house very cool. This is a common effect in stone houses and barns as they stay closer to the average daily/weekly tempature because it takes a long time for the tempature of that much mass to change.