> And there is a lot more energy spent heating in the north than there is cooling in the south.
Source for this?
Source for this?
And you need heating non-stop in winter, while in the summer half of the day is enough many times.
Also, most people have heating, but only some AC.
Or weave sealed cells of a phase-change material with high thermal mass that melts at around 33 degC into your fabric, and freeze the garment before wearing it. This makes possible a thick, heavy jacket that you can wear to keep cool.
I suppose the vapor pressure could be lower than that for water, if there were effectively none in the air already. That would only be more effective than sweat on very humid days. You would be wetting your wet bulb with two different liquids.
The trick is to find one better than water that is also non-toxic, non-flammable, non-carcinogenic, and non-polluting. It would almost be easier to just remove all that water from the surrounding humid air, so that sweating works to cool you down again....
The phase-change material between liquid and solid would work better, but still requires a separate cooling technology to "recharge" it. And phase-change material still works better in building walls than in clothing. So you're right back to keeping your whole building cool, rather than a specific person.
You could also strap a personal radiator to your back, but no one wants to work on the tropical plantation in the first place, much less do it inside spacesuit-like apparel.
Can you recommend one suitable for regular use?
There are a few liquids that would work. One example is the refrigerant HCFC-124. However, all of these liquids are chlorofluorocarbons, and cause much more damage to the atmosphere than any amount of A/C usage. Pretty much all volatile organic compounds fall into at least one of three categories: flammable, toxic, highly potent greenhouse gas.
For instance, you wouldn't want to smell like a ton of bananas all the time, or drive honeybees into a frenzy every time you pass by.
Gas heating is something like 90% efficient now.
People, stop. Downvoting doesn't change facts.
Heat pumps have a higher EER, but also higher parasitic losses, which is the source of confusion on the whole thread.
It's like claiming that rockets are "more efficient" than cars because they move you faster.
And the bottom line is that for the same unit of energy used to generate 1 BTU from resistance heating, we can move several BTUs.
EDIT: I'd also like to note that heat pump systems which include resistance heating systems will typically mark them as "emergency heating". Because they are less efficient, unless it's so brutally cold outside that the heat pump has dropped below 1 EER or can't even operate properly.
EDIT2: I forgot that the units in SEER are not the same on both sides of the ratio. (That is, it's not actually a ratio, since those are supposed to be unitless.) So my original "13+ BTUs" was high. Changed it to a non-descript weasel-word instead.
Narrow interpretations of definitions to support a point don’t actually provide much useful insight to the topic being discussed, and are seen as distracting. So these non-useful comments are being downvoted to make them less visible. It is not an issue of whether they are technically correct.
You could probably make an interesting point about the electrical efficiency of heat pumps, or you could make a comment about terminology and explain that “technically” the correct term is X, but instead you chose to interpret a term in a way that contradicts the contextually obvious meaning and then base an argument on top of that.
"arrow interpretations of definitions to support a point don’t actually provide much useful insight to the topic being discussed, and are seen as distracting. So these non-useful comments are being downvoted to make them less visible. It is not an issue of whether they are technically correct."
Except, I'm not arguing for or against a "point", only that the terminology was wrong. But it does matter, because it leads to confusion, and if you stop to think about it for longer than it takes to jab at the downvote button, the reason why it matters is interesting.
It's not that people here are thinking about the subject carefully, they're just disagreeing reflexively.
Voting isn't specifically for correctness/incorrectness, but encompasses many things. In this specific case, I think the voting reasoning or on your comments can be likely be summarized as "is the comment contributing usefully to the discussion, or providing useful or insightful information in some other way". I think people aren't viewing your comments in this discussion as providing that, and some people may believe they are actually the opposite.
> Heating via electrical resistance is 100% efficient. All energy goes into generating heat. There is no loss.
This sounds a bit coy, doesn’t it? It’s a bit suspicious that heat pumps are completely omitted from your comment, and it’s also a bit suspicious that explicit discussion about terminology is omitted, and instead the definitions are included as a presumption. Putting the main point of your argument into a presumption of the actual text of your argument is nothing short of poor form (i.e. rude) if done purposefully, and the rest of the argument built on top of these presuppositions is boring and uninformative.
If you can imagine a better approach, consider discussing the terminology and definitions directly, and then explaining why sloppy terminology can cause confusion. You have still not explained why the terminology is so important here. Instead, you’ve made the following statements:
> …if you stop to think about it for longer than it takes to jab at the downvote button, the reason why it matters is interesting.
> It's not that people here are thinking about the subject carefully, they're just disagreeing reflexively.
Consider whether these statements make claims about the internal thought processes of people who disagree with you, and whether making claims about how other people think will further whatever goals you have commenting on this site.
The problem is, the terminology is only wrong if you take an extremely narrow approach of "heating" being "generating heat". But it's quite obvious that we are discussing heating of an enclosed space. And it doesn't actually matter at all whether that heat being placed into the closed space was generated from raw energy within the enclosed space, or moved from externally into the enclosed space. And if there is no difference between these two options, you can achieve greater than 100% efficiency between energy-spent and heat-provided by moving the heat.
I often find that it surprised people to realize that a heat pump is effectively >100% efficient.
No, this is quite wrong. You're not taking into account generation and transmission losses. Gas heat is actually much more efficient than electrical resistance heating.
Plus, as others are saying, using energy to move heat from one place to another allows you to move more heat than you could generate just by converting the energy to heat.
It is nice to know that the conversion from electricity to heat is effectively 100% efficient and we are really making a cost comparison instead.
They use a lot of energy when they turn on initially, after that, its very little . Ive been working on smart thermostats that take advantage of this phenomenon to lower HVAC costs.
AFAIK, the most efficient residential systems are ductless split systems, where you basically have a centralized compressor and distributed air handlers in individual rooms. This allows for variable flow and localized control, which reduces need.
[0] https://en.wikipedia.org/wiki/Seasonal_energy_efficiency_rat...
> But when either replacing equipment, or specifying new installations, a variety of SEERs are available. For most applications, the minimum or near-minimum SEER units are most cost effective, but the longer the cooling seasons, the higher the electricity costs, and the longer the purchasers will own the systems, the more that incrementally higher SEER units are justified.
So if you are cooling a house to 70 degrees in 90 degree weather, you are fighting a 20 degree difference.
If you are heating a house to 70 degrees in 30 degree weather, you are fighting a 40 degree difference.
In a severe heatwave, you might spend weeks with much of the day at 100 degrees; during a cold snap last winter, there was a span where I live where the temperature was usually around 0, and never higher than 10 degrees.
Meanwhile, a furnace works by directly converting energy to heat; for simplicity, let's assume a heater generates 1 unit of heat for 1 unit of energy (it's 100% efficient).
An air-conditioner, however, moves heat, moving heat from inside to outside. An air conditioner doesn't use 1 unit of energy to move 1 unit of heat; an air conditioner might move 3 units of heat using 1 unit of energy.
So putting the two together, it takes roughly 6 times as much energy to heat my house on the coldest days as it does to cool my house on the hottest days.
The full answer is a lot more complicated than that, because other things in houses are generating waste heat and you need to look at the deviations above and below your target temperature range over the full year and across many different places. Someone else has already posted a link to US energy usage showing that total energy spent on air conditioning is a fraction of that spent on heating, but from the above you should be able to get an intuitive feel for why that's so.
Be careful, you're angering the thermo gods! If that was true, I would simply use an air-conditioner to heat my house. Cool, the outside and move the heat inside. In reality, you have the efficiencies backwards. Cooling is more energy intensive than heating.
It's true, and people do. Install a heat pump, and save your traditional heat source for when it's sufficiently cold outside.
So run that system backwards for heating, and you would at only use twice the energy for heating. That said, you can typically cut your heating bill in half using ASHP, with it losing efficiency as the outside temperature decreases. It rarely goes below a COP of 1, so it makes sense to use in place of resistance heating.
However that assumes that you must use electricity for heating. Using wood for heating, you are using a renewable resource that is cheaper for every unit of heat you get.
Even then you have to be willing to keep the thermostat set at 55F/13C or the resistive heaters are going to kick in.
That is not to say gas isn't cheaper.
I know, that sounds crazy, and sometimes the CoP is given as an "efficiency", which makes it sound even crazier — a CoP of 2.0 is "200% efficient"! But it's not science fiction; it's a simple consequence of the Carnot cycle being reversible and the Carnot efficiency of heat engines at ordinary temperatures being quite low.
http://iopscience.iop.org/article/10.1088/1748-9326/8/1/0140...
So why speculate and not use data instead?
Look at your bills and use the price of kilowatt of electricity and the price of CCF or MCF of natural gas to calculate the cost of MBTU. The above study came to a conclusion that you will use 3.5 MBTUs in MN for each 1 MBTU spent in FL.
In my case 1 kWt cost ~10c, 1 MCF of natural gas costs ~$12. At these prices 15 SEER AC will require ~$6.67 for 1 MBTU of cooling 95% Efficient Nat gas furnace will require ~$12.63 for 1 MBTU of heating.
Can you do the rest of the math?
No you don't. I don't know anyone who leaves their heating on at night. In the winter I run my heating for a few hours a day maybe.
I usually drink 4-6 litres of tap water while at work, and I have to use a personal heater at my desk to keep warm in winter (my co-workers complain if I set the thermostat higher). When it's summer, especially when it's 35+ degrees (95 F), I'm in heaven.
In fact, the coldest I've ever felt in my life (and I've lived in cold places like Moscow) was the one time as a silly freshman in college, when I drank just under a gallon of water (couldn't quite finish it) in under a minute on a dare. So very cold, and nothing could warm me up. Just had to wait it out.
Water drinking contests, along with overhydration during/after intense physical exertion (e.g. marathons, partying on MDMA), account for nearly all known cases of death from water intoxication.