The best thing we took away from our tests was the chance at a direct comparison between a single-hose design and a dual-hose design that were otherwise identical, and our experience confirmed our suspicions that dual-hose portable ACs are slightly more effective than single-hose models but not effective enough to make a real difference
I roll to disbelieve. I think it is much more likely that something is wrong with their test setup than that the difference between one-hose and two-hose is negligible.
Just on priors, the most obvious problem is that they’re testing somewhere which isn’t hot outside the room—either because they’re inside a larger air-conditioned building, or because it’s not hot outdoors. Can we check that?
Well, they apparently tested it in April 2022, i.e. nowish, which is indeed not hot most places in the US, but can we narrow down the location more? The photo is by Michael Hession, who apparently operates near Boston. Daily high temps currently in the 50′s to 60′s (Fahrenheit). So yeah, definitely not hot there.
Now, if they’re measuring temperature delta compared to the outdoors, it could still be a valid test. On the other hand, if it’s only in the 50′s to 60′s outside, I very much doubt that they’re trying to really get a big temperature delta from that air conditioner—they’d have to get the room down below freezing in order to get the same temperature delta as a 70 degree room on a 100 degree day.
If they’re only trying to get a tiny temperature delta, then it really doesn’t matter how efficient the unit is. For someone trying to keep a room at 70 on a 100 degree day, it’s going to matter a lot more.
So basically, I am not buying this test setup. It does not look like it is actually representative of real usage, and it looks nonrepresentative in the basically the ways we’d expect from a test that found little difference between one and two hoses.
Generalizable lesson/heuristic: the supposed “experts” are also not even remotely trustworthy.
(Also, I expect it to seem like I am refusing to update in the face of any evidence, so I’d like to highlight that this model correctly predicted that the tests were run someplace where it was not hot outside. Had that evidence come out different, I’d be much more convinced right now that one hose vs two doesn’t really matter.)
(Also, I expect it to seem like I am refusing to update in the face of any evidence, so I’d like to highlight that this model correctly predicted that the tests were run someplace where it was not hot outside. Had that evidence come out different, I’d be much more convinced right now that one hose vs two doesn’t really matter.)
Over the course of a sweltering summer week in Boston, we set up our five finalists in a roughly 250-square-foot space, taking notes and rating each model on the basic setup process, performance, portability, accessories, and overall user experience.
ETA: it’s not clear that’s the same testing setup used in the other tests they described. But they do talk about how the 1-vs-2 convertible unit “struggled to make the room any cooler than 70 degrees” which sounds like it was probably reasonably hot.
Alright, I am more convinced than I was about the temperature issue, but the test setup still sounds pretty bad.
First, Boston does not usually get all that sweltering. I grew up in Connecticut (close to Boston and similar weather), summer days usually peaked in the low 80′s. Even if they waited for a really hot week, it was probably in the 90′s. A quick google search confirms this: typical July daily high temp is 82, and google says “Overall during July, you should expect about 4-6 days to reach or exceed 90 F (32C) while the all-time record high for Boston was 103 F (39.4C)”.
It’s still a way better test than April (so I’m updating from that), but probably well short of keeping a room at 70 on a 100 degree day. I’m guessing they only had about half that temperature delta.
Second, their actual test procedure (thankyou for finding that, BTW):
Over the course of a sweltering summer week in Boston, we set up our five finalists in a roughly 250-square-foot space, taking notes and rating each model on the basic setup process, performance, portability, accessories, and overall user experience.
The makers of portable air conditioners are required to list their performance and efficiency statistics, and our research and our previous testing have proven these numbers to be accurate. By prescreening for these stats, we got the impression that every model we tested would cool a room capably. We confirmed that they did by taking measurements with two Lascar temperature and humidity data loggers—we placed one 3 feet away, directly in front of the unit, and placed the other one 6 feet away on a diagonal. With each AC set to its lowest setting (between 60 and 64 degrees Fahrenheit, depending on the unit) and the highest fan/compressor setting, we measured the temperature and humidity in the room every 15 minutes for three hours to see how well each unit dispersed the coolness and dehumidification process across the space.
Three feet and six feet away? That sure does sound like they’re measuring the temperature right near the unit, rather than the other side of the room where we’d expect infiltration to matter. I had previously assumed they were at least measuring the other side of the room (because they mention for the two-hose recommendation “In our tests, it was also remarkably effective at distributing the cool air, never leaving more than a 1-degree temperature difference across the room”), but apparently “across the room” actually meant “6 feet away” based on this later quote:
In our tests, it [a two-hose air conditioner] produced some of the most even and consistent cooling across the room, never registering more than a 1-degree difference between our monitors positioned at 3 feet directly in front of the AC and 6 feet away on a diagonal.
… which sure does sound more like what we’d expect.
So I’m updating away from “it was just not hot outside”—probably a minor issue, but not a major one. That said, it sure does sound like they were not measuring temperature across the room, and even just between 3 and 6 feet away the two-hose model apparently had noticeably less drop-off in effectiveness.
Boston summers are hotter than the average summers in the US, and I’d guess are well above the average use case for an AC in the US. I agree having two hoses are more important the larger the temperature difference, and by the time you are cooling from 100 to 70 the difference is fairly large (though there is basically nowhere in the US where that difference is close to typical).
I’d be fine with a summary of “For users who care about temp in the whole house rather than just the room with the AC, one-hose units are maybe 20% less efficient than they feel. Because this factor is harder to measure than price or the convenience of setting up a one-hose unit, consumers don’t give it the attention it deserves. As a result, manufacturers don’t make as many cheap two-hose units as they should.”
Does anyone in-thread (or reading along) have any experiments they’d be interested in me running with this air conditioner? It doesn’t seem at all hard for me to do some science and get empirical data, with a different setup to Wirecutter, so let me know.
Added: From a skim of the thread, it seems to me the experiment that would resolve matters is testing in a large room with temperature sensors more like 15 feet away in a city or country that’s very hot outside, and to compare this with (say) Wirecutter’s top pick with two-hoses. Confirm?
… I actually already started a post titled “Preregistration: Air Conditioner Test (for AI Alignment!)”. My plan was to use the one-hose AC I bought a few years ago during that heat wave, rig up a cardboard “second hose” for it, and try it out in my apartment both with and without the second hose next time we have a decently-hot day. Maybe we can have an air conditioner test party.
Predictions: the claim which I most do not believe right now is that going from one hose to two hose with the same air conditioner makes only a 20%-30% difference. The main metric I’m interested in is equilibrium difference between average room temp and outdoor temp (because that was the main metric relevant when I was using that AC during the heat wave). I’m at about 80% chance that the difference will be over 50%.
(Back-of-the-envelope math a few years ago said it should be roughly a factor-of-two difference, and my median expectation is close to that.)
I also expect (though less strongly) that, assuming the room’s doors and windows are closed, corners of the room opposite the AC in single-hose mode will be closer to outdoor temp than to the temp 3 ft away from the AC, and that this will not be the case in two-hose mode. I’d put about 60% on that prediction.
These predictions are both conditional on the general plan I had, and might change based on details of somebody else’ test plan. In particular, some factors I expect are relevant:
The day being hot enough and the room large enough that the AC runs continuously (as opposed to getting the room down to target temperature easily, at which point it will shut off until the temperature goes back up).
The test room does not open into an indoor room at lower temperature (I had planned to open the outside door and windows in the rest of the apartment).
Test room generally not in direct sun, including outside of walls/ceiling. If it is in full sun, then I’d strengthen my probability for the second prediction.
Also, in case people want to bet, I should warn that I did use this AC during a heat wave a few years ago (with just the one hose), so e.g. I have seen firsthand how it tends to only cool the space right in front of it. On the other hand, it could turn out that was due to factors specific to the apartment I was in back then—for instance, the roof in that apartment was uninsulated and in full sun, so a lot of heat came off the ceiling.
I would have thought that the efficiency lost is roughly (outside temp—inside temp) / (exhaust temp—inside temp). And my guess was that exhaust temp is ~130.
I think the main way the effect could be as big as you are saying is if that model is wrong or if the exhaust is a lot cooler than I think. Those both seem plausible; I don’t understand how AC works, so don’t trust that calculation too much. I’m curious what your BOTEC was / if you think 130 is too high an estimate for the exhaust temp?
If that calculation is right, and exhaust is at 130, outside is 100, and house is 70, you’d have 50% loss. But you can’t get 50% in your setup this way, since your 2-hose AC definitely isn’t going to get the temp below 65 or so. Maybe most plausible 50% scenario would be something like 115 exhaust, 100 outside, 85 inside with single-hose, 70 inside with double-hose.
I doubt you’ll see effects that big. I also expect the improvised double hose will have big efficiency losses. I think that 20% is probably the right ballpark (e.g. 130/95/85/82). If it’s >50% I think my story above is called into question. (Though note that the efficiency lost from one hose is significantly larger than the bottom line “how much does people’s intuitive sense of single-hose AC quality overstate the real efficacy?”)
Your AC could also be unusual. My guess is that it just wasn’t close to being able to cool your old apartment and that single vs double-hoses was a relatively small part of that, in which case we’d still see small efficiency wins in this experiment. But it’s conceivable that it is unreasonably bad in part because it has an unreasonably low exhaust temp, in which case we might see an unreasonably large benefit from a second hose (though I’d discard that concern if it either had similarly good Amazon reviews or a reasonable quoted SACC).
I’m curious what your BOTEC was / if you think 130 is too high an estimate for the exhaust temp?
I don’t remember what calculation I did then, but here’s one with the same result. Model the single-hose air conditioner as removing air from the room, and replacing with a mix of air at two temperatures: TC (the temperature of cold air coming from the air conditioner), and TH (the temperature outdoors). If we assume that TC is constant and that the cold and hot air are introduced in roughly 1:1 proportions (i.e. the flow rate from the exhaust is roughly equal to the flow rate from the cooling outlet), then we should end up with an equilibrium average temperature of TC+TH2. If we model the switch to two-hose as just turning off the stream of hot air, then the equilibrium average temperature should drop to TC.
Some notes on this:
It’s talking about equilibrium temperature rather than power efficiency, because equilibrium temperature on a hot day was mostly what I cared about when using the air conditioner.
The assumption of roughly-equal flow rates seems to be at least the right order of magnitude based on seeing this air conditioner in operation, though I haven’t measured carefully. If anything, it seemed like the exhaust had higher throughput.
The assumption of constant TC is probably the most suspect part.
Ok, I think that ~50% estimate is probably wrong. Happy to bet about outcome (though I think someone with working knowledge of air conditioners will also be able to confirm). I’d bet that efficiency and Delta t will be linearly related and will both be reduced by a factor of about (exhaust—outdoor) / (exhaust—indoor) which will be much more than 50%.
… and will both be reduced by a factor of about (exhaust—outdoor) / (exhaust—indoor) which will be much more than 50%.
I assume you mean much less than 50%, i.e. (T_outside—T_inside) averaged over the room will be less than 50% greater with two hoses than with one?
I’m open to such a bet in principle, pending operational details. $1k at even odds?
Operationally, I’m picturing the general plan I sketched four comments upthread. (In particular note the three bulleted conditions starting with “The day being hot enough and the room large enough that the AC runs continuously...”; I’d consider it a null result if one of those conditions fails.) LMK if other conditions should be included.
Also, you’re welcome to come to the Air Conditioner Testing Party (on some hot day TBD). There’s a pool at the apartment complex, could swim a bit while the room equilibrates.
I studied the impact of infiltration because of clothes dryers when I was doing energy efficiency consulting. The nonobvious thing that is missing from this discussion is that the infiltration flow rate does not equal the flow rate of the hot air out the window. Basically absent the exhaust flow, there is an equilibrium of infiltration through the cracks in the building equaling the exfiltration through the cracks in the building. When you have a depressurization, this increases the infiltration but also decreases the exfiltration. If the exhaust flow is a small fraction of the initial infiltration, the net impact on infiltration is approximately half as much as the exhaust flow. The rule of thumb for infiltration is it produces about 0.3 air changes per hour, but it depends on the temperature difference to the outside and the wind (and the leakiness of the building). I would guess that if you did this in a house, the exhaust flow would be relatively small compared to the natural infiltration. So roughly the impact due to the infiltration is about half as much as the calculations indicate. But if you were in a tiny tight house, then the exhaust flow would overwhelm the natural infiltration and the increase in infiltration would be close to the exhaust flow.
Another factor is the dehumidification load on the air conditioner. This is a really big deal in the southeastern US, though it would be less of a deal in the Bay Area. Basically, if it is very humid outside, the additional infiltration air has to be de-humidified, and that can double how much heat the air conditioner needs to remove from the infiltration air. So this could counteract the benefit of the net infiltration being smaller than the exhaust flow.
The exhaust temperature of 130°F sounds high to me for regular air conditioner, but heat pumps designed to heat hot water and dry clothing to go even higher than that. So it is possible they increase it more than a regular air conditioner to increase the overall efficiency (because the fan energy is significantly larger with the hose as compared to a typical window unit). Still, I am confident that the reduction in efficiency of one hose versus two hose is less than 50% unless it is very hot and humid outside.
If the building is ending up around 70, that means I’m underestimating the exhaust quantity by about 2x. But then apparently the extra infiltration is only about half of the exhaust. So sounds like the errors cancel out and my initial estimate happens to be roughly right?
Tc does seem like a bad assumption. I tried instead assuming a constant difference between the intake and the cold output, and the result surprised me. (The rest of this comment assumes this model holds exactly, which it definitely doesn’t).
Let Tr be the temperature of the room (also intake temperature for a one-hose model). Then at equilibrium,
Tr=(Tc+Th)/2
Tr=((Tr−Δ)+Th)/2
2Tr=Tr+Th−Δ
Tr=Th−Δ
i.e. no loss in cooling power at all! (Energy efficiency and time to reach equilibrium would probably be much worse, though)
In the case of an underpowered (Δ=15) one-hose unit handling a heat wave (Th=100), you’d get Tr=85 and Tc=70—nice and cool in front of the unit but uncomfortably hot in the rest of the room, just as you observed. Adding a second hose would resolve this disparity in the wrong direction, making Tr=Tc=85. So if you disproportionately care about the area directly in front of the AC, adding the second hose could be actively harmful.
Also, like, Berkeley heat waves may just significantly different than, like, Reno heat waves. My current read is that part of the issue here is that a lot of places don’t actually get that hot so having less robustly good air conditioners is fine.
I think labeling requirements are based on the expectation of cooling from 95 to 80 (and I expect typical use cases for portable AC are more like that). Actually hot places will usually have central air or window units.
I roll to disbelieve. I think it is much more likely that something is wrong with their test setup than that the difference between one-hose and two-hose is negligible.
Just on priors, the most obvious problem is that they’re testing somewhere which isn’t hot outside the room—either because they’re inside a larger air-conditioned building, or because it’s not hot outdoors. Can we check that?
Well, they apparently tested it in April 2022, i.e. nowish, which is indeed not hot most places in the US, but can we narrow down the location more? The photo is by Michael Hession, who apparently operates near Boston. Daily high temps currently in the 50′s to 60′s (Fahrenheit). So yeah, definitely not hot there.
Now, if they’re measuring temperature delta compared to the outdoors, it could still be a valid test. On the other hand, if it’s only in the 50′s to 60′s outside, I very much doubt that they’re trying to really get a big temperature delta from that air conditioner—they’d have to get the room down below freezing in order to get the same temperature delta as a 70 degree room on a 100 degree day.
If they’re only trying to get a tiny temperature delta, then it really doesn’t matter how efficient the unit is. For someone trying to keep a room at 70 on a 100 degree day, it’s going to matter a lot more.
So basically, I am not buying this test setup. It does not look like it is actually representative of real usage, and it looks nonrepresentative in the basically the ways we’d expect from a test that found little difference between one and two hoses.
Generalizable lesson/heuristic: the supposed “experts” are also not even remotely trustworthy.
(Also, I expect it to seem like I am refusing to update in the face of any evidence, so I’d like to highlight that this model correctly predicted that the tests were run someplace where it was not hot outside. Had that evidence come out different, I’d be much more convinced right now that one hose vs two doesn’t really matter.)
From how we tested:
ETA: it’s not clear that’s the same testing setup used in the other tests they described. But they do talk about how the 1-vs-2 convertible unit “struggled to make the room any cooler than 70 degrees” which sounds like it was probably reasonably hot.
Alright, I am more convinced than I was about the temperature issue, but the test setup still sounds pretty bad.
First, Boston does not usually get all that sweltering. I grew up in Connecticut (close to Boston and similar weather), summer days usually peaked in the low 80′s. Even if they waited for a really hot week, it was probably in the 90′s. A quick google search confirms this: typical July daily high temp is 82, and google says “Overall during July, you should expect about 4-6 days to reach or exceed 90 F (32C) while the all-time record high for Boston was 103 F (39.4C)”.
It’s still a way better test than April (so I’m updating from that), but probably well short of keeping a room at 70 on a 100 degree day. I’m guessing they only had about half that temperature delta.
Second, their actual test procedure (thankyou for finding that, BTW):
Three feet and six feet away? That sure does sound like they’re measuring the temperature right near the unit, rather than the other side of the room where we’d expect infiltration to matter. I had previously assumed they were at least measuring the other side of the room (because they mention for the two-hose recommendation “In our tests, it was also remarkably effective at distributing the cool air, never leaving more than a 1-degree temperature difference across the room”), but apparently “across the room” actually meant “6 feet away” based on this later quote:
… which sure does sound more like what we’d expect.
So I’m updating away from “it was just not hot outside”—probably a minor issue, but not a major one. That said, it sure does sound like they were not measuring temperature across the room, and even just between 3 and 6 feet away the two-hose model apparently had noticeably less drop-off in effectiveness.
Boston summers are hotter than the average summers in the US, and I’d guess are well above the average use case for an AC in the US. I agree having two hoses are more important the larger the temperature difference, and by the time you are cooling from 100 to 70 the difference is fairly large (though there is basically nowhere in the US where that difference is close to typical).
I’d be fine with a summary of “For users who care about temp in the whole house rather than just the room with the AC, one-hose units are maybe 20% less efficient than they feel. Because this factor is harder to measure than price or the convenience of setting up a one-hose unit, consumers don’t give it the attention it deserves. As a result, manufacturers don’t make as many cheap two-hose units as they should.”
Does anyone in-thread (or reading along) have any experiments they’d be interested in me running with this air conditioner? It doesn’t seem at all hard for me to do some science and get empirical data, with a different setup to Wirecutter, so let me know.
Added: From a skim of the thread, it seems to me the experiment that would resolve matters is testing in a large room with temperature sensors more like 15 feet away in a city or country that’s very hot outside, and to compare this with (say) Wirecutter’s top pick with two-hoses. Confirm?
… I actually already started a post titled “Preregistration: Air Conditioner Test (for AI Alignment!)”. My plan was to use the one-hose AC I bought a few years ago during that heat wave, rig up a cardboard “second hose” for it, and try it out in my apartment both with and without the second hose next time we have a decently-hot day. Maybe we can have an air conditioner test party.
Predictions: the claim which I most do not believe right now is that going from one hose to two hose with the same air conditioner makes only a 20%-30% difference. The main metric I’m interested in is equilibrium difference between average room temp and outdoor temp (because that was the main metric relevant when I was using that AC during the heat wave). I’m at about 80% chance that the difference will be over 50%.
(Back-of-the-envelope math a few years ago said it should be roughly a factor-of-two difference, and my median expectation is close to that.)
I also expect (though less strongly) that, assuming the room’s doors and windows are closed, corners of the room opposite the AC in single-hose mode will be closer to outdoor temp than to the temp 3 ft away from the AC, and that this will not be the case in two-hose mode. I’d put about 60% on that prediction.
These predictions are both conditional on the general plan I had, and might change based on details of somebody else’ test plan. In particular, some factors I expect are relevant:
The day being hot enough and the room large enough that the AC runs continuously (as opposed to getting the room down to target temperature easily, at which point it will shut off until the temperature goes back up).
The test room does not open into an indoor room at lower temperature (I had planned to open the outside door and windows in the rest of the apartment).
Test room generally not in direct sun, including outside of walls/ceiling. If it is in full sun, then I’d strengthen my probability for the second prediction.
Also, in case people want to bet, I should warn that I did use this AC during a heat wave a few years ago (with just the one hose), so e.g. I have seen firsthand how it tends to only cool the space right in front of it. On the other hand, it could turn out that was due to factors specific to the apartment I was in back then—for instance, the roof in that apartment was uninsulated and in full sun, so a lot of heat came off the ceiling.
I would have thought that the efficiency lost is roughly (outside temp—inside temp) / (exhaust temp—inside temp). And my guess was that exhaust temp is ~130.
I think the main way the effect could be as big as you are saying is if that model is wrong or if the exhaust is a lot cooler than I think. Those both seem plausible; I don’t understand how AC works, so don’t trust that calculation too much. I’m curious what your BOTEC was / if you think 130 is too high an estimate for the exhaust temp?
If that calculation is right, and exhaust is at 130, outside is 100, and house is 70, you’d have 50% loss. But you can’t get 50% in your setup this way, since your 2-hose AC definitely isn’t going to get the temp below 65 or so. Maybe most plausible 50% scenario would be something like 115 exhaust, 100 outside, 85 inside with single-hose, 70 inside with double-hose.
I doubt you’ll see effects that big. I also expect the improvised double hose will have big efficiency losses. I think that 20% is probably the right ballpark (e.g. 130/95/85/82). If it’s >50% I think my story above is called into question. (Though note that the efficiency lost from one hose is significantly larger than the bottom line “how much does people’s intuitive sense of single-hose AC quality overstate the real efficacy?”)
Your AC could also be unusual. My guess is that it just wasn’t close to being able to cool your old apartment and that single vs double-hoses was a relatively small part of that, in which case we’d still see small efficiency wins in this experiment. But it’s conceivable that it is unreasonably bad in part because it has an unreasonably low exhaust temp, in which case we might see an unreasonably large benefit from a second hose (though I’d discard that concern if it either had similarly good Amazon reviews or a reasonable quoted SACC).
I don’t remember what calculation I did then, but here’s one with the same result. Model the single-hose air conditioner as removing air from the room, and replacing with a mix of air at two temperatures: TC (the temperature of cold air coming from the air conditioner), and TH (the temperature outdoors). If we assume that TC is constant and that the cold and hot air are introduced in roughly 1:1 proportions (i.e. the flow rate from the exhaust is roughly equal to the flow rate from the cooling outlet), then we should end up with an equilibrium average temperature of TC+TH2. If we model the switch to two-hose as just turning off the stream of hot air, then the equilibrium average temperature should drop to TC.
Some notes on this:
It’s talking about equilibrium temperature rather than power efficiency, because equilibrium temperature on a hot day was mostly what I cared about when using the air conditioner.
The assumption of roughly-equal flow rates seems to be at least the right order of magnitude based on seeing this air conditioner in operation, though I haven’t measured carefully. If anything, it seemed like the exhaust had higher throughput.
The assumption of constant TC is probably the most suspect part.
Ok, I think that ~50% estimate is probably wrong. Happy to bet about outcome (though I think someone with working knowledge of air conditioners will also be able to confirm). I’d bet that efficiency and Delta t will be linearly related and will both be reduced by a factor of about (exhaust—outdoor) / (exhaust—indoor) which will be much more than 50%.
I assume you mean much less than 50%, i.e. (T_outside—T_inside) averaged over the room will be less than 50% greater with two hoses than with one?
I’m open to such a bet in principle, pending operational details. $1k at even odds?
Operationally, I’m picturing the general plan I sketched four comments upthread. (In particular note the three bulleted conditions starting with “The day being hot enough and the room large enough that the AC runs continuously...”; I’d consider it a null result if one of those conditions fails.) LMK if other conditions should be included.
Also, you’re welcome to come to the Air Conditioner Testing Party (on some hot day TBD). There’s a pool at the apartment complex, could swim a bit while the room equilibrates.
I studied the impact of infiltration because of clothes dryers when I was doing energy efficiency consulting. The nonobvious thing that is missing from this discussion is that the infiltration flow rate does not equal the flow rate of the hot air out the window. Basically absent the exhaust flow, there is an equilibrium of infiltration through the cracks in the building equaling the exfiltration through the cracks in the building. When you have a depressurization, this increases the infiltration but also decreases the exfiltration. If the exhaust flow is a small fraction of the initial infiltration, the net impact on infiltration is approximately half as much as the exhaust flow. The rule of thumb for infiltration is it produces about 0.3 air changes per hour, but it depends on the temperature difference to the outside and the wind (and the leakiness of the building). I would guess that if you did this in a house, the exhaust flow would be relatively small compared to the natural infiltration. So roughly the impact due to the infiltration is about half as much as the calculations indicate. But if you were in a tiny tight house, then the exhaust flow would overwhelm the natural infiltration and the increase in infiltration would be close to the exhaust flow.
Another factor is the dehumidification load on the air conditioner. This is a really big deal in the southeastern US, though it would be less of a deal in the Bay Area. Basically, if it is very humid outside, the additional infiltration air has to be de-humidified, and that can double how much heat the air conditioner needs to remove from the infiltration air. So this could counteract the benefit of the net infiltration being smaller than the exhaust flow.
The exhaust temperature of 130°F sounds high to me for regular air conditioner, but heat pumps designed to heat hot water and dry clothing to go even higher than that. So it is possible they increase it more than a regular air conditioner to increase the overall efficiency (because the fan energy is significantly larger with the hose as compared to a typical window unit). Still, I am confident that the reduction in efficiency of one hose versus two hose is less than 50% unless it is very hot and humid outside.
Thanks! It’s amusing that we had this whole discussion and the one commenter who knew what they were talking about got just one upvote :)
It sounds very plausible that exhaust is small relative to natural infiltration and I believe you that (extra infiltration) = 50% (exhaust).
In the other direction, it looks like I was wrong about 130 degrees and we’re looking at more like 100 (alas, googling random forum comments is an imperfect methodology, though I do feel it’s plausible that John’s AC has unusually cold exhaust).
If the building is ending up around 70, that means I’m underestimating the exhaust quantity by about 2x. But then apparently the extra infiltration is only about half of the exhaust. So sounds like the errors cancel out and my initial estimate happens to be roughly right?
Tc does seem like a bad assumption. I tried instead assuming a constant difference between the intake and the cold output, and the result surprised me. (The rest of this comment assumes this model holds exactly, which it definitely doesn’t).
Let Tr be the temperature of the room (also intake temperature for a one-hose model). Then at equilibrium,
Tr=(Tc+Th)/2
Tr=((Tr−Δ)+Th)/2
2Tr=Tr+Th−Δ
Tr=Th−Δ
i.e. no loss in cooling power at all! (Energy efficiency and time to reach equilibrium would probably be much worse, though)
In the case of an underpowered (Δ=15) one-hose unit handling a heat wave (Th=100), you’d get Tr=85 and Tc=70—nice and cool in front of the unit but uncomfortably hot in the rest of the room, just as you observed. Adding a second hose would resolve this disparity in the wrong direction, making Tr=Tc=85. So if you disproportionately care about the area directly in front of the AC, adding the second hose could be actively harmful.
Also, like, Berkeley heat waves may just significantly different than, like, Reno heat waves. My current read is that part of the issue here is that a lot of places don’t actually get that hot so having less robustly good air conditioners is fine.
I bought my single-hose AC for the 2019 heat wave in Mountain View (which was presumably basically similar to Berkeley).
When I was in Vegas, summer was just three months of permanent extreme heat during the day; one does not stay somewhere without built-in AC in Vegas.
I think labeling requirements are based on the expectation of cooling from 95 to 80 (and I expect typical use cases for portable AC are more like that). Actually hot places will usually have central air or window units.
Sweet! I could also perform a replication I guess.
Or you could get to it before I do and I could perform a replication.