Heat Pumps – The Well-Tempered Future of A/Cs • Hacker News Board

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#41

Post by elil17 » Wed, Jul 05, 2023, 4:51 PM UTC

__MatrixMan__ wrote: post #15

I live in a colder climate where heat pumps are not popular. After talking with a number of HVAC people about this I was surprised to learn that despite being very similar to an AC system in principle, in practice converting an AC system into a heat pump system doesn't make economic sense--you end up just ripping one out and installing the other. I don't fully understand why this is the case, but I hope that there's…

There's no reason you couldn't just switch a couple valves out in your AC and perhaps change the refrigerant to make it into a serviceable heat pump. However, you'd need to retrofit controls/electronics, which I don't think most HVAC technicians would know how to do. It's also not advisable to attempt to DIY something like this because it is very easy to accidentally vent the refrigerant, which is a very potent greenhouse gas.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#42

Post by metiscus » Wed, Jul 05, 2023, 4:51 PM UTC

cyfex wrote: post #5

nottorp wrote: post #3

Isnt any a/c a heat pump though?

I have never really understood the difference between a heat pump and an A/C myself. Any expert care to explain it in layman's terms?

In physics we call a device that uses the compression and expansion of a fluid to move heat between parts of a system a heat pump.

An air conditioner uses a compressor to convert a refrigerant and sends the compressed fluid through a condenser. The condenser rejects heat from the system into the environment. This is the component of an air conditioner that is found outside. The compressed fluid is then passed through an expansion valve and into an evaporator where it is allowed to expand. Expansion is a process that requires heat. The heat flows into the expanding fluid from the environment inside the home. Air is blown across the evaporator coils to transfer heat energy from the home into the fluid which is then returned outside.

A heat pump is capable of reversing the flow of heat energy. The flow of fluid is reversed from an air-conditioner using something called a reversing valve. The compressor sends compressed fluid into the home where heat is rejected through the evaporator coil. The fluid then flows into the condenser coil and is allowed to expand outside, drawing in heat from the outside environment. The heated fluid is then returned to the compressor and the cycle continues.

In HVAC terminology an Air Conditioner is a one way physical heat pump and a heat pump is a bidirectional physical heat pump. Hopefully that helps clear it up a bit.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#43

Post by nottorp » Wed, Jul 05, 2023, 4:52 PM UTC

Moto7451 wrote: post #9

nottorp wrote: post #3

Isnt any a/c a heat pump though?

Compared to a traditional air conditioning unit, the reversing valve is the major difference. Your standard AC can only move heat from indoors to outdoors. A heat pump can do the reverse to warm your space. My basement heat pump is rated to provide heat even when it’s -20F outside.

Pretty sure all acs sold here can reverse and heat a bit.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#44

Post by ericd » Wed, Jul 05, 2023, 4:52 PM UTC

silisili wrote: post #10

digdugdirk wrote: post #2

Well this was an oddly terrifying introductory paragraph for an IEEE article: "... half of Phoenix residents are at risk of an emergency room visit or worse if their electricity fails during a future heat wave, according to a recent study. Air conditioning is what keeps people there comfortable—and alive—a growing fraction of the year. The extreme heat already kills hundreds of Phoenix-area residents every year, a nu…

Sure, but it can happen anywhere. I was just reading yesterday about a person who died in Portland of heat during the dome. Same with cold weather, if the gas/electric goes out during the winter. There's really only a few places one can live with moderate enough weather to avoid those scenarios.

And that's why you see fireplaces/stoves in a lot of houses in the northeast, even if they have gas/electric heat.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#45

Post by genmud » Wed, Jul 05, 2023, 4:52 PM UTC

digdugdirk wrote: post #2

Well this was an oddly terrifying introductory paragraph for an IEEE article: "... half of Phoenix residents are at risk of an emergency room visit or worse if their electricity fails during a future heat wave, according to a recent study. Air conditioning is what keeps people there comfortable—and alive—a growing fraction of the year. The extreme heat already kills hundreds of Phoenix-area residents every year, a nu…

Luckily, the local grid here in AZ is fairly robust, probably one of the best in the US. During the 3 years I lived in DC area, I probably had 3 or 4 power outages due to weather (ranging from a couple hours to multiple days).

In the 30+ years I have lived in Arizona, I have experienced probably 2 outages, lasting a total of a few hours (one was when a car hit a transformer, the other was when a microburst knocked a bunch of aging poles down).

The last outage I had was like 6-8 years ago.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#46

Post by retrac » Wed, Jul 05, 2023, 4:52 PM UTC

cmrdporcupine wrote: post #12

digdugdirk wrote: post #2

Well this was an oddly terrifying introductory paragraph for an IEEE article: "... half of Phoenix residents are at risk of an emergency room visit or worse if their electricity fails during a future heat wave, according to a recent study. Air conditioning is what keeps people there comfortable—and alive—a growing fraction of the year. The extreme heat already kills hundreds of Phoenix-area residents every year, a nu…

I've read a few times that the population of the entire US south only really started to grow in earnest once AC was invented. Ah, here's an article: https://www.nytimes.com/2017/08/04/upshot/the-all-conquering... It's pretty crazy because growing up in central/northern Alberta, I never even really encountered air conditioning until I was into my early 20s and moved to southern Ontario (where living without it would b…

I've likewise read arguments that AC is linked to the substantial economic growth in the second half of the 20th century, in regions like southern France, southern Japan, and the southern United States. All regions that historically lagged economically behind their culturally and economically similar more northern counterpart regions. Hard to say how much of a factor, but there has to be some truth to it: just imagine productivity in a Texas factory at 40 °C and 90% humidity vs. 25 °C and 50% humidity.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#47

Post by 1-more » Wed, Jul 05, 2023, 4:52 PM UTC

Maxburn wrote: post #23

nottorp wrote: post #3

Isnt any a/c a heat pump though?

It's an industry term for mechanical equipment that can heat AND cool. One piece of equipment replaces your AC AND heat source. Heat pumps in particular are getting a push from "green" initiatives because they only use electricity for fuel which can potentially be supplied by "renewable" sources. ie; it's a buzz word.

> because they only use electricity for fuel which can potentially be supplied by "renewable" sources.

They also can operate at >100% efficiency. Under the right conditions (I'll let someone who knows more about it fill that in) they can provide more heat than the same amount of power going into a resistive heater (which is I think per-se 100% efficient right?). Kinda wild.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#48

Post by elil17 » Wed, Jul 05, 2023, 4:53 PM UTC

nightski wrote: post #26

__MatrixMan__ wrote: post #15

I live in a colder climate where heat pumps are not popular. After talking with a number of HVAC people about this I was surprised to learn that despite being very similar to an AC system in principle, in practice converting an AC system into a heat pump system doesn't make economic sense--you end up just ripping one out and installing the other. I don't fully understand why this is the case, but I hope that there's…

The thing is (especially where I live) I'd still need a gas furnace. We regularly see -20F to -40F in the winter. While the 95% scenario sounds great, in practice still needing gas means we still need all the gas infrastructure. From my understanding natural gas burns pretty clean. The problem is leaks in infrastructure and drilling, which isn't going away because I buy a heat pump.

Although natural gas is "clean" compared to, say, coal, the advantage of a heat pump is that it uses less total energy than natural gas. That means it would be more efficient to run a heat pump off a natural gas power plant than to burn natural gas to heat your home directly.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#49

Post by samtho » Wed, Jul 05, 2023, 4:53 PM UTC

cyfex wrote: post #5

nottorp wrote: post #3

Isnt any a/c a heat pump though?

I have never really understood the difference between a heat pump and an A/C myself. Any expert care to explain it in layman's terms?

An A/C works almost identical to your refrigerator. Using a closed loop of refrigerant with specific thermal properties, it will remove heat from one side and emit heat from the other.

If you are able to run this system backwards, you could in theory swap which side is a heat sink (the cold side) and heat source (the hot side). While a traditional A/C cannot do this, heat pumps can electronically switch which side of the system is collecting the heat and which side is releasing it.

This is an improvement over resistive heating (think space heater) because we’re not pumping electricity into some filament that resists current flow and emits off heat due to the resistance. Instead, we are taking heat from inside and moving it out or taking heat from outside and moving it in.

Fun fact, a resistive heating device is a rare case of something being 100% electrically efficient in that all the energy it uses will be turned into heat, whereas heat normally is a byproduct of imperfect conductors, which everything is, and is therefore considered wasted energy in almost all other applications.

Re: Heat Pumps – The Well-Tempered Future of A/Cs

#50

Post by metiscus » Wed, Jul 05, 2023, 4:53 PM UTC

ramesh31 wrote: post #34

Swamp coolers are massively underutilized as well. The vast majority of residential cooling in all but the most humid climates can be done with nothing but a fan and some cold water; no compressed gases necessary.

The issue with swamp coolers (evaporative cooling) is that you need relatively low humidity for them to work and they increase the humidity of the interior cooled environment. If you use them in combination with an air conditioner, they will very likely reduce the efficiency of the air conditioner by increasing the dehumidification load of the air conditioner.