2 Common Comfort Problems Caused by Air Conditioning
No, that’s not an art installation or a privacy screen. What you’re looking at in the photo above is a hotel room I stayed in recently. Behind the chair and the ironing board is the air conditioning system. The bed was right behind me as I took the picture. Do you know which of the many common comfort problems I was trying to fix?
Problem 1: Air flow
I placed the chair and ironing board right there to deflect the air flow. In the bed, I felt a strong, cold breeze that shot right across the room. It was quite uncomfortable. With the deflectors in place, I didn’t feel much of the air flow and was much happier. I played with the fan speed to see if lowering it would help, but it didn’t. Only the deflectors helped.
This experience, which I’m sure is common in many homes as well, is the result of HVAC designers and installers not following one of the cardinal rules of HVAC design: Don’t blow air on people. If you click that link, you’ll see that that is the first of 17 things I listed to improve duct systems.
Yes, cool air blowing on you can feel nice if you’re exercising, sitting in a warm room, or having a hot flash. Generally, though, it’s not a recipe for comfort.
If you have heating and cooling vents in your home with this problem, you may be able to adjust the louvers to deflect the air. If that doesn’t work, you could try changing to a different kind of register. For example, if you have the type shown below, you can change the direction of air flow by adjusting the horizontal louvers in back and the vertical louvers in front. (This one is the Hart & Cooley 618.)
If that doesn’t do it for you, try something like the 2-way supply register shown below (Hart & Cooley 682).
Now, what about the other of the two common comfort problems?
Problem 2: System size
The second problem in my hotel room was the capacity of the air conditioner. As is true for most hotel rooms, the cooling load was low and the AC was oversized. That meant that it would come on for a few minutes and then go off. So I was repeatedly throwing the covers off and then covering up again throughout the night.
That problem isn’t quite as easy to fix after the fact…unless you’re ready to replace the air conditioning system. If that’s the case, go read my article about how to find out what size AC you need without doing a heating and cooling load calculation. If that doesn’t work—or if you’re building new and want to avoid this problem from the start—you can get a full load calculation and equipment selection. (We do that and so do other companies.)
But it’s not just a smaller system that could help. Choosing one that operates in two or more stages or with variable capacity is a great option. It can still have the maximum capacity you’ll need for the hot days but can ramp down to cover the many, many more hours of lower temperatures (also known as part-load conditions). That helps it run longer, evening out the indoor temperature. Pretty much all of the HVAC systems we design at Energy Vanguard are of the multi-stage or variable capacity types.
Do you have either of these two common comfort problems in your home?
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel.
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Hah, the ironing board is a great deflector and almost always available in a hotel room, good one.
I wonder if I can figure out how to hang one to deal with the ubiquitous “mini-split above the bed, unavoidably pointing straight at me” issue :). Probably fall on me while sleeping, which might defeat the point!
Enjoy these hotel room observation posts.
James: Doesn’t your ductless controller allow you to change how the vanes move? The Mitsubishi units we have in our office and that I have at home all do that.
Yeah, that can help, but limited range (freeze my head or my toes? My partner’s head or toes?)
My issue with your #2 problem is the “Eco” mode for fan speed (which is really what you experienced). I first experienced this many years ago in a motel my wife and I were in during some severe thunderstorms. The fan (and compressor) only turned on when the thermostat triggered it, greatly increasing room noise and sending a cold wave of air into the room – until it stopped. All night long. I could not set the fan to run continuously, which would have provided a continuous “white” noise (that would have helped drown out the thunder) and help remove room moisture as the refrigerant coils continued to condense moisture as they slowly warmed. We currently have a window unit with similar settings; I always set the fan to “Low” for those very reasons.
David: This was the first hotel room I’ve been in that didn’t allow for continuous fan operation. Then last week I was in another.
while you are at it, pull out the iron and sit it near the board and you can have reheat
Andy: That’s quite a Smart idea! :~)
Allison,
Therma-HEXX has the radiant cooling problem along with condensation solved. We just completed our first project of many to come, with your latent system design by Sophie, using a CERV2 and dehumidifier in parallel with our high performance ThermaPANEL hydronic radiant heat and cooling system in CT and it is working perfectly.
Robert: I’ll have to talk with Sophie and get the scoop. It sounds interesting. I’m also interested in seeing how well it performs, so keep us updated.
Will do Allison. I would like to chat with you sometime and go over our system and why it is so effective. Our new interior product brochure can be viewed here:
https://therma-hexx.com/applications/interior-radiant-heating-cooling/
I’m forwarding this post to Hurricane Erin… Two rules… Don’t blow air on people and don’t be an oversized system!
Heh heh heh! Slightly different context, but it works there, too, Chris.
I think I stayed at the same hotel as Allison. The thermostat was located remotely from the PTAC and it resulted in long cycle times which felt like about a 5 F temperature swing.
Beware of enabling continuous fan. It might reduce the temperature swings, but it can result in significantly higher humidity levels in humid climates due to water evaporating off the indoor coil during the off cycle once that coil warms up.
I am not a fan of ductless systems because of this problem. Having the supply and return at the same location does not work well for achieving good air circulation. Many of the units use moving vanes to alleviate this problem, but I would still rather have ducts with multiple supply vents and separated return air paths for better air circulation.
RoyC: Continuous fan was not an option on the PTAC in that room. I have used it in the past, though, but mostly as white noise to drown out noisy neighbors.
Just returned from four days at Cedar Point on Lake Erie. When I walked into our Sandusky hotel room I noticed the through the wall hvac unit was not blowing directly onto the beds. I was relieved to see that.
The unit kept the room at the set point, but the blower never shut off. It had the choice of high or low but not auto. The humidity was very high and very uncomfortable. The tile floors were sticky and the bath towels would not dry. I asked the front desk if they would have someone look at the unit, they replied they would. No change in the fan it continued to run continuously. The humidity remained high , we just dealt with it. When I checked out, the clerk asked how was our stay, when I told her the room was humid.
The clerk responded oh, I’ll credit you two nights.
I didn’t expect that!
Jim: I’ve also had the experience of get free nights and even moved to a fancy suite when I tell hotel staff about problems like that. One time they couldn’t move me to another room, so they had someone replace the PTAC. I wrote about that here:
Have You Seen What’s in Your Hotel Room Air Conditioner?
https://www.energyvanguard.com/blog/Have-You-Seen-What-s-in-Your-Hotel-Room-Air-Conditioner
My wife and I visit a Florida resort yearly the utilizes in-wall fan coil units with high level discharge louvers. Inevitably the louvers are directed towards the bed area. So I learned to bring a small wrench with me on these travels and readjust the louvers upward and toward the wall area. Makes a huge difference in comfort.
Mark: Well, that’s another way to tackle the problem.
The ‘premium’ (incremental added cost) of inverter / variable speed compressor window shakers is now down to about $200-300 (Midea, LG, GE). That makes a world of difference in both comfort and efficiency and provides quick payback in energy cost.
We can only hope that variable speed compressors and smart air flow controls (i.e. those that pay attention to humidity) make their way to the notoriously uncomfortable and inefficient world of hotel room PTACs!
That said, I find it irksome that the cost increment to go variable compressor capacity on typical residential ducted systems remains at several thousand dollars…seems an opportunity for some disruptive newcomer to the industry!