How inefficient are portable air conditioners?
When I was at my in laws last weekend, I noticed that they were using a portable air conditioner to cool the upstairs. The unit is described at: http://www.delonghi.com/en-us/products/comfort/air-conditioning/portable-air-conditioners/pinguino-air-to-air-pac-an125hpekc-0151801211. Apparently, their central air conditioning system doesn’t do a good job of cooling the second floor (which is only used when they have guests). The unit struck me as a seriously compromised way of accomplishing space conditioning. Am I missing something or is the concept of operation seriously flawed?
The unit gets placed near a window. A single hose expels hot air out the window. That expelled air must come from the conditioned space because there is no provision to draw air from anywhere else. There is no drain for condensate. With a little online research, I found that it sprays the condensate on the condenser so it evaporates and is expelled out the single hose. It seems to me that this device would induce infiltration elsewhere in the house that would undo a significant fraction of the cooling that is accomplished. The manual explains that efficiently is measured using EER, but doesn’t specify an EER value. Instead, the manual states that EER doesn’t apply to portable air conditioners because they are not regulated by DOE. Calculating an EER from the maximum cooling and the maximum power draws comes out about 9.5. I suspect the maximum cooling rating doesn’t factor in the induced infiltration.
I suppose that, from a purely economic standpoint, it may make sense for my in-laws because they use the upstairs infrequently. In that application, first cost is much more important than operating efficiency. Even so, inefficiency bothers me.
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Replies
Reid,
I agree with your analysis. I'm not very impressed by the installation instructions, which include the advice shown in the illustration below.
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My in-laws are pretty typical air conditioning consumers. They bought the unit, "installed" it, turned it on, and then the room got cold. Like most consumers, they wouldn't think any more deeply than that about how it works. They have a double hung window, so their setup wasn't quite as awful as the picture you reproduced above.
Another incident made me think about typical consumers. We were sitting on the porch and my father-in-law commented about how bad the neighbor's air conditioner is. "They need a new AC. It runs almost all of the time." He was quite proud of the fact that his central AC ran less than half of the time. (The temperature was above design temperature that day.)
Inefficient, Loud, HEAVY.
We purchased one few years ago in an attempt to cool a master bedroom while we spent the month of July arguing with a home warranty company over an inoperable HVAC system.
My unit had also had the hose (as seen in Martin's pic) but the end was designed to span the width of a typical double hung window and create a seal. Needless to say these units are not suitable for those who have casement windows.
It's worse than just an efficiency problem- it's also a diminishing capacity problem. At 70F indoors, 90F outdoors, about half the rated capacity is gone(!). So whatever the standalone COP of the system is, the parasitic loads cut the as-used efficiency in half when outdoor temps hit the 90s.
A dual-hose portable AC vendor (taking only outdoor air into the condenser coil, not room air) lays it out fairly suscintly here:
http://www.climax-air.com/dual-hose-portable/
I had never really looked at portable air conditioners, but had assumed that they were all dual hose, since the deficiencies of using a single hose approach are DEAD OBVIOUS, even without running the math on it.
There are other vendors of dual hose portable AC units but marketing fluff usually doesn't explain it effectively eg:
https://www.friedrich.com/products/commercial/portable/zoneaire
Obviously it's better to have a heat pump build into the house, but that's not always possible for various reasons. In any case, a portable air conditioner is a much more economical winter solution than an electric heater.
I'm currently living in the Far North of New Zealand in a rented three bedroom cottage of fairly old construction. I'm only 35.5º S, near the ocean, and have delicious bananas growing in the garden.
I work from home, so want a comfortable "office" environment all day and evening.
There is a wood stove which I think puts out in the region of 8-10 kW of heat. That is certainly my cheapest option for heating, with the 3 m^3 of wood I used last winter costing around US$150 split, dried, and delivered. Unfortunately much of the time it is simply too powerful.
Also of course it does nothing in summer when, without taking any action, it's going to be quite a few degrees warmer inside than the 28-30 C outside in the afternoons. It can easily be 35 C inside with windows closed. You can keep the inside temperature closer to the outside temperature by opening windows (with insect screens!) but then you lose control of humidity, which is often very high here.
I have a Dimplex portable air conditioner rated at 4 kW heating / 4 kW cooling. When operating it uses 1100 W of electricity. I also have a Panasonic dehumidifier which I use on automatic setting summer and winter to keep the humidity around 50%. That uses about 350W. I lead the Dimplex's hose out a window that slides horizontally, using the supplied expanding panel and some tape to seal the gaps.
The Dimplex has a place to attach a water drain hose, and also a small tank that holds maybe two cups of water. I first got it during very hot and humid February 2022 weather and was having to empty the tank three or four times a day, but since I started running my dehumidifier (which has a 5l tank) at the same time, even in summer, I've never had to empty the Dimplex again.
It takes about 30 seconds to take the louvers off one port, the hose off the other port, spin the unit 180º, and reattach the hose and louvers in the opposite ports. And hit the mode button to change the thermostat between heating and cooling (the mechanical operation of the unit is the same either way). Mostly it just stays untouched in one mode all summer or all winter, but there have been very occasional changeable days where I've reconfigured it twice.
In summer I set it to 24 C which probably does keep it around 24 where it is in the kitchen, but at my work area on the other side of an open plan area (and around a corner) it stays at a quite steady 24.9 unless the day is so hot that it simply can't cope and runs continuously. I haven't seen over 26, even when it's 30 outside and super sunny and the thing is running continuously from 2 PM to 7 PM.
This year I recorded the daily electricity usage of the portable air conditioner for most of January, using the popular Poniie PN2000 (which I think is better than the Kill-A-Watt).
13 Jan 2.60 kWh
14 Jan 5.82 kWh
15 Jan 2.45 kWh
16 Jan 2.53 kWh
17 Jan 0.55 kWh
18 Jan 0.42 kWh
19 Jan 2.05 kWh (cold day ... heating)
20 Jan 2.50 kWh (heating)
21 Jan 7.23 kWh only 23C but very humid
22 Jan 7.13 kWh
23 Jan 6.78 kWh
24 Jan 4.97 kWh
25 Jan 8.42 kWh thunderstorms, constant rain, very humid, 21 C or so at night, so AC all night.
26 Jan 8.45 kWh
27 Jan 2.99 kWh
28 Jan 1.63 kWh
29 Jan 3.82 kWh
30 Jan 4.07 kWh
31 Jan 6.12 kWh
I then switched to recording the dehumidifier power usage in February:
01 Feb 1.33 kWh
02 Feb 0.30 kWh
03 Feb 1.94 kWh
04 Feb 0.22 kWh
05 Feb 0.37 kWh
06 Feb 0.16 kWh
07 Feb 0.79 kWh
08 Feb 0.64 kWh
09 Feb 0.58 kWh
10 Feb 1.89 kWh
11 Feb 1.14 kWh
14 Feb 2.12 kWh (3 days)
20 Feb 14.92 kWh (6 days)
25 Feb 4.52 kWh (5 days)
27 Feb 0.96 kWh (2 days)
In general, the dehumidifier is using around 0.5 kWh per day in fine summer weather, 2-3 kWh in very rainy weather. The water tank needs to be emptied roughly around every 2.5 kWh of electricity usage -- quite constant since between the dehumidifier and the air conditioner, both on automatic control, there is very little variation in either temperature or humidity. Running continuously (as it will for a couple of months in a place that has never been dehumidified ... or not since the previous winter) it uses 8 kWh/day (and, yes, need emptying three times), so the above figures are all very part time -- typically 1-3 hours a day, up to 6-9 hours in wet weather
In term of efficiency, of course you lose something from the single hose design of the air conditioner. I keep a window on the far corner of the house open a few inches, on the cool (south) side. Still, you are constantly drawing in (in summer) hot and humid air, which then has to be cooled and dried. Also, in summer the dehumidifier creates more heat for the air conditioner to get rid of. In winter they work together. I think the dehumidifier's 350W of electricity usage is producing about 900W of heating.
But still, over those measurement periods I've used on average 4.24 kWh/day for the air conditioner and 1.18 kWh/day for the dehumidifier. Different time periods, but similar weather, so I think the 5.42 kWh/day is fairly representative for summer.
Most of that usage is at around US$0.18/kWh, but the air conditioner does run quite a bit in the first half of the evening 5-9 PM peak time when the price is US$0.35/kWh. Neither unit normally runs during the morning peak time. I'm going to estimate there were 8 days in that January period in which 2 kWh was used in that peak time, costing $0.34/day more than if peak time had been avoided, or on average $0.10/day overall.
So my average cooling cost in peak summer (Jan/Feb) is around 5.42*0.18 + 0.10 = US$1.075/day or $32.27 for a 30 day month.
My total household electricity use in January was 424.5 kWh (13.7/day), and in February so far (25 days) 416 kWh (16.6/day). In spring and autumn when I'm using neither heating nor cooling I use around 9-10 kWh/day, about 4 from hot water heating, 1 from the fridge, and 3 from my several computers.
I actually use slightly less electricity in winter, except perhaps July, which in 2024 was 536 kWh (17.3/day). In June I could not use the fire, because I hadn't gotten it inspected/serviced and had to wait for an appointment, and used 780 kWh (26/day). I use the portable air conditioner and dehumidifier if the outside temperature is above about 10 C in calm(ish) weather, 12 C if it's windy. Below that I light the fire, roughly 50 nights a year and maybe 5-10 times in daytime. Average winter temperature is 15 C in the day time (can be anything from 10-20) and 8 C at night. As previously mentioned I use about $150 of wood a year.
My total electricity usage in 2024 was 4904 kWh (13.4/day) of which 902 kWh was during my "free" hour leaving 4002 kWh (10.9/day) charged for. I manage to get all my dish washing and clothes washing and maybe 2/3 of my water heating done in the free hour.
So in conclusion I think the portable air conditioner is a reasonable solution for me, given my renting situation (and failure to persuade the landlord to install a fixed heat pump), and the low $400 initial cost.