> What's the average monthly leccy bill in Phoenix during the summer? $400?
The average high temperature in Phoenix in July is 106.5F (41.4C). If you are cooling to 70.0F (21.1C), that's a difference of 36.5F (20.3C).
The average January low in Berlin is 28.0F (-2.2C). If you are heating to 65.0F (18.3C), that's a difference of 37.0F (20.5C).
I feel like many people living in climates that don't require air conditioning have this view that it's fantastically inefficient and wasteful. Depending on how you are heating (e.g. if you are using a gas boiler), cooling can be significantly more efficient per degree of difference. Especially if you don't have to dehumidify the air, as in Phoenix.
You’re ignoring one critical difference between these two scenarios. Humans, and all human related activities, produce heat as a waste product. It’s much easier, and consumes less additional energy, to heat an occupied space, than to cool it. Thanks to the fact that your average human produces 80W of heat just to stay alive.
So every human in your cold space is 80W fewer watts of energy you need to produce to heat the space. But in a hot space, it’s an extra 80W that needs to be removed.
Add to that all of the appliances in a home. It’s not unusual for a home to be drawing 100W of electricity just keep stuff powered on in standby, and that’s another 100W of “free” heating. All of this is before we get to big ticket items, like hobs, ovens, water heaters etc.
So cooling a living space is always more costly than heating a living space. Simply because all the waste energy created by people living in the space reduces the total heating requirement of the space, but equally increases the cooling requirement of that same space.
All of this is ignoring the fact that it’s easy to create a tiny personal heated environment around an individual (it’s called a woolly jumper). But practically impossible to create a cool individual environment around a person. So in cold spaces you don’t have to heat everything up to same temperature for the space to be perfectly liveable, but when cooling a space, you have to cool everything, regardless of if it’ll impact the comfort of the occupants.
> So cooling a living space is always more costly than heating a living space. Simply because all the waste energy created by people living in the space reduces the total heating requirement of the space, but equally increases the cooling requirement of that same space.
This simply is not true for a furnace or electric resistive heat.
My furnace produces 0.9W of heat for every 1W of energy input. More efficient ones do 0.98, the best you get with electric resistive heat is 1W.
On the other hand my air conditioner moves 3.5W of heat outside for every 1W of energy input.
My AC works in both directions, in winter it moves more cold outside than the power it consumes. Not sure what the factor is exactly, but I think same as for cooling.
Thermodynamics unfortunately disagree. As your temperature deltas get smaller efficiency goes down.
"Thermodynamics" is singular :) As for the numbers, my AC's manual shows COP of 3.71 for heating and 3.13 for cooling.
So you are spot on, in winter temperature deltas are larger, and efficiency goes up.
Those high COPs are probably for relatively small temperature deltas. Heat pumps get _less_ efficient when the temperature deltas are larger. See page 18 of the manual linked below for an example. As the temperature gets lower, the heating COP gets lower. The same should be the case with cooling (higher outdoor temperatures lead to lower COPs), but the data is not presented in the same way.
https://backend.daikincomfort.com/docs/default-source/produc...
You are saying that heat pumps get less efficient when deltas are larger, and the parent post says they get more efficient when deltas are larger. In a sense, you're both correct.
There are multiple relevant temperatures for a heat pump, and the pump is more efficient when some of those are higher and some lower. A heat pump has two heat exchangers, one on the inside of the building and one outside. Each of those heat exchangers has two temperatures: the refrigerant loop temperature at that point, and the ambient temperature (air for air source heat pumps, ground for ground source heat pumps). There's also a fifth relevant temperature that has indirect influence: the setpoint (the desired indoor ambient temperature).
Efficiency increases when the temperature delta between the refrigerant and ambient temperatures is higher (both indoor and outdoor). But those temperature deltas vary inversely with the delta between the indoor and outdoor ambient temperatures.
So, in summary:
- Heat pumps get less efficient when the temperature delta between indoor and outdoor temperature is higher.
- They get more efficient when the temperature delta between refrigerant and ambient temperature is higher.
The net effect of this is that heat pumps become less efficient as the temperature becomes hotter outside in the summer and colder outside in the winter.
Correct!
You can also think about it as far as actually moving heat. Cold is the absence of heat, and so when the air is colder, there is less heat moved for the same effort and you have to work harder -- less efficiently -- for the same amount of head to get moved.
I see, the previous commenter stated the opposite :). Anyway, both numbers are > 1.
> "Thermodynamics" is singular :)
> plural in form but singular or plural in construction
(https://www.merriam-webster.com/dictionary/thermodynamics)
I think American and British English treat words like this differently.
"cooling a living space is always more costly than heating a living space" Man I wish this was true but it definitely isn't in anyplace that gets significantly cold. Heat pumps are super super efficient at cooling but they get less efficient at heating the colder it gets. Humans and appliances create a pretty negligible amount of heat.
> "cooling a living space is always more costly than heating a living space" Man I wish this was true but it definitely isn't in anyplace that gets significantly cold. Heat pumps are super super efficient at cooling but they get less efficient at heating the colder it gets. Humans and appliances create a pretty negligible amount of heat.
I thought any place that is significantly cold can still dig underground and at some point you can get enough heat to run your heat pump?
Right, but that's expensive too (initial outlay and maintenance) and needs to win a lot of efficiency before it pays off.
Yeah, if you have a bare minimum of 30k burning a hole in your pocket and enough open land to drill the well with the correct geology, and the larger your house the bigger/more wells you need as you're drawing from the Earth's relatively constant temperature. So the only way to get more heat is to get more surface area for the coolant.
Some people on reddit are reporting quotes of 125k for larger (>3000 sq ft) houses.
As someone who lives in a 4-season environment that can get down into the single digits F on occasion in the winter (forecast to be there for a couple of days next week), and has an air-source heat pump, I just suck it up and eat the $400-$500/month heating costs for the auxiliary (electric resistive) heat in Dec/Jan/Feb. If someone gifts me a ground-sourced heat pump I'll gladly accept, but I've got kids to raise so setting aside money for one is a long way off.
Heating is more costly if you use technology created for cooling. When you try to cool a cold space in order to heat hot space, you will have a bad time. You could use electric heater for heating, it should have no problems with heating, but will use more electricity. Or you could use something actually cheaper, like wood or fossil fuels. If you use more expensive method (like electricity) it will be more expensive.
This might be true for you. I have lived with free wood for heating and it was more expensive for me than using a heat pump. What is expensive depends on a lot of factors, political, social, location, time and knowledge. It is not a clear dollar per delta T.
Chopping up a tree is kind of fun, we bill that to the entertainment budget instead of the heating budget. And it usually happens during a hotter season, so I might have to go inside to take a break, get a cool drink. So, we can bill some of the tree chopping activity to the cooling budget!
I also point out that Phoenix's "summer" last longer than Berlin's winter:
https://weatherspark.com/y/75981/Average-Weather-in-Berlin-G...
https://weatherspark.com/y/2460/Average-Weather-in-Phoenix-A...
The figure you are looking for is heating/cooling degree-days.
For each day, use the average high and the average low. Subtract the desired maximum dwelling temperature from the average high: if the result is positive, add it to the cooling degree-days total. Subtract the average low from the from the minimum dwelling temperature: if the result is positive, add it to the heating degree-days total.
Over a year, that gives you comparable figures on how much you will need to cool or heat the space. Many agencies calculate this for specific areas.
Here, for example, are the current season numbers for Boston: https://www.massenergymarketers.org/resources/degree-days/bo...
Generic regional numbers for the US: https://www.eia.gov/energyexplained/units-and-calculators/de...
Cooling takes less energy per BTU moved vs heating. In AC/heat pumps that's represented by SEER rating for cooling and HSPF rating for heating (heat pumps). Modern ACs have SEER ratings for 20+ and HSPF ratings for 8+. What it means is that on average, spending 1 BTU equivalent of electrical energy cools down the house by 20 BTU. Similarly for heat pump it means spending 1 BTU of electricity heats up the house by 8 BTU. Electric resistive heating is equivalent of HSPF 1.
Also in sunny climates it's easy to use solar energy for cooling making it carbon net-zero. Cold places typically burn natural gas for heating, it's much harder to make heating carbon net-zero.
A lot of what you said is intuitively/directionally correct, but misses a lot of important physics related to heat transfer in buildings and operational questions of space heating equipment.
This is your most accurate/relevant point:
> All of this is ignoring the fact that it’s easy to create a tiny personal heated environment around an individual (it’s called a woolly jumper).
Whereas this is plainly wrong:
> It’s much easier, and consumes less additional energy, to heat an occupied space, than to cool it.
And then the following is correct but the marginal reduction in load is minimal except in relatively crowded spaces (or spaces with very high equipment power densities):
> Thanks to the fact that your average human produces 80W of heat just to stay alive.
The truth is it is generally easier to cool not heat when you take into account the necessary energy input to achieve the desired action on the psychrometric chart, assuming by “ease” you mean energy (or emissions) used, given that you are operating over a large volume of air - which does align with your point about the jumper to be fair!
Generally speaking, an A/C uses approx. 1 unit of electricity for every 3 units of cooling that it produces since it uses heat transfer rather than heat generation (simplified ELI5). It is only spending energy to move heat, not make it. On the other hand, a boiler or furnace or resistance heat system generally uses around 1 unit of input energy for every 0.8-0.9 units of heating energy produced. Heat pumps achieve similar to coefficients of performance as A/Cs, because they are effectively just A/Cs operating in reverse.
Your point about a jumper is great, but there are local cooling strategies as well (tho not as effective), eg using a fan or an adiabatic cooling device (eg a mister in a hot dry climate).
> So cooling a living space is always more costly than heating a living space.
Once you move to cost, it now also depends on your fuel prices, not just your demand and system type. For instance, in America, nat gas is so cheap, that even with its inefficiencies relative to a heat pump, if electricity is expensive heating might still be cheaper than cooling per unit of thermal demand (this is true for instance in MA, since electricity is often 3x the price of NG). On the other hand, if elec is less than 3x the cost of nat gas, then cooling is probably cheaper than heating per unit of demand, assuming you use natural gas for your heating system.
It is true that heat is easier to generate. Berlin is considered mild while Phoenix is considered very hot. They just happen to have the same temperature deltas. On the whole, the world spends many, many times more energy heating living spaces than cooling them. The coldest cities people live in just have much larger room temperature deltas than the hottest.
I'm reading this discussion while smh. Looking at a high temperature of -10F on Sunday!
This is a good point that I had not considered, and I will add a few additional thoughts:
* In cold weather, solar heat gain can work in your favor as well. Much of the effect will depend on the orientation, shading, and properties of your windows, though. On the other hand, as another commenter pointed out, more sun in southern, cooling-dominated climate can also mean more, cheaper electricity.
* If you have a heat pump water heater, it will actually _cool_ your space significantly. The heat is transferred from your home to your water and mostly goes down the drain with it.
* At 65F (18.3C), most people I know would already be wearing a jumper/sweater. That's why I chose a lower target temperature for Berlin. The best source I could find[1] indicates that in November-December of 2022 (in the context of rising energy prices due to Russia's war with Ukraine), Germans actually kept their houses at 19.4C, on average.
* Maybe I'm moving the goalposts a bit, but I chose Berlin mostly because the numbers worked out conveniently. As someone who grew up in the American upper midwest, I wouldn't consider Berlin to be particularly cold. Phoenix, on the other hand, is the hottest city in the country and its summers are some of the hottest in the world. In general, the hottest cities are still closer to what we'd consider room temperature than the coldest are.
[1] https://www.cleanenergywire.org/news/80-percent-german-house... (original report is on German)
There’s some element of comfort vs necessity here, I think… really, people could be keeping their houses at, like… 55F and they’d be totally fine. They just need to get acclimated to it.
On the other hand, depending on the humidity, heats over like 85F start becoming a health risk for some activities.
As someone acclimated to warmer weather, I disagree. People work outside in 85, 90, 95° weather without health problems all the time. Hydrate and your body will acclimate.
I live in Phoenix and construction , HVAC, landscapers etc work in the summer here when it is 110+.
Depends on the humidity. Sweating is more efficient in less humid climates IIRC.
> So cooling a living space is always more costly than heating a living space
Nope. That's precisely wrong. Tl;dr heating normally uses less efficient technology than cooling and has to work across a higher temperature difference.
In Alberta or Minnesota, where the delta in the winter can be as high as 60 degrees centigrade (-40 outside, +20 inside) but only 20 degrees centigrade at most in the summer (+45 outside, +25 inside), heating is far more costly. Even accounting for waste heat from appliances. Most heating is done with furnaces, not heat pumps. Air conditioners are heat pumps and are 3x as efficient as a furnace. There are also less energy intensive cooling methods - shading, fans, swamp coolers - commonly used in the developing world and continental Europe.
On the other hand in a place with warm winters and hot summers, such as south east Asia, obviously cooling is more expensive because heating is unnecessary.
The highest temperature ever recorded is around 60 degrees centrigrade, a mere 23 degrees above the human body. The low temperature record is like -90, 127 degrees below body temperature. Needing to heat large deltas is way more common than needing to cool high deltas. And cooling is done with heat pumps, which are more efficient than the technologies used most commonly for heating (resistive or combustion).
> when cooling a space, you have to cool everything, regardless of if it’ll impact the comfort of the occupants.
Keep the house at 25 degrees centigrade and run a ceiling fan. 23 if you're a multi-millionaire. You'll be far more comfortable outdoors if your house is closer to the outside temperature. The North American need to have sub-arctic temperatures in every air conditioned space in the summertime is bizarre (don't even get me started on ice water).
100%. And can be wonderfully done by efficient heatpumps that cover the warmer months too. Also nice correlation between hot and sunny areas which means solar can get you to net zero pretty quick. (Says man looking at his solar panels right now covered with snow.)
you cannot win this argument with the average person who lives in a chilly European country. it just does not compute.
there are whole important cultural lifeways related to opening and closing windows at proper times for efficient cooling and ventilation. these work really well — in Europe — and are treasured traditions.
getting people to accept AC is sort of like trying to convince the average American to go grocery shopping on a bicycle. some may accept the idea but only the most European influenced already.
There's a big gap between "accept AC" and "build a megapolis in a city named after a bird that bursts into flames."
Phoenix is a slow-rolling disaster regardless of whether it's easier to heat or cool a room to comfort.
This is such an interesting perspective that I've never thought about. Thanks!
Recently it was -7C where I lived. Even without heating, my indoor temp didn't go below 15C. In regions where cold temperatures are common, isolation and heat retaining materials are very common. Is preventing heat gain as simple as preventing heat loss?
Yes, insulation works both ways. My garage is unheated and insulated. If I go out there to work on something in the winter I always compare the temperature outside. On a sunny day it might be pleasant outside and freezing in my garage - so I'll open the door and let it warm up.
Insulation makes the house more resistance to temperature change (relative to the inside and outside).
One thing people forget is the delta is very different in the summer and winter. Lets say your thermostat is on 70 year round. If it is 100 degrees out you only have to cool 30 degrees. When it is 0 F out you have a delta of 70 degrees. So for this scenario, expect to use more energy in the winter.
a greenhouse can heat a space by enough to be comfortable for free, but not cool it. Windows and sunlight matter.