Comments on: My Undersized Mini-Split Heat Pump in a Heat Wave

By: Tricia

Tricia — Wed, 26 Apr 2023 16:00:02 +0000

Thank you for this article. Most info on heat pump is about performance in cold winter weather. I live in coastal Georgia, so I’m more concerned about the heat and humidity in the summer. From this article, a right-sized heat pump is a good option for me when I replace my AC and ancient gas furnace.

By: Robin W Boyd

Robin W Boyd — Sun, 30 Oct 2022 01:14:46 +0000

Equipment ratings have become more confusing due to manufacturers having to appease government regulations in most countries. For a mini-split system with inverter technology, you want to focus on rated capacity and sensible capacity at full capacity of the range. If the total capacity is 36,000 Btu and the sensible capacity at full operation is 31,000 Btu, the difference in capacity between the two is the latent capacity of cooling that will go into condensing moisture from the air. If Australasia is as arid as I am thinking, you can lean on the total capacity more so than sensible since there won’t be as much latent capacity used to remove humidity. Hope this helps.

By: Chris Edwards

Chris Edwards — Tue, 25 Oct 2022 02:05:06 +0000

I’m trying to right-size a replacement mini-split heat pump for my house, but I’m not sure how exactly to interpret the “rated capacity” and “capacity range” figures that manufacturers specify. Rated capacity seems to be actual measured output under some standard test conditions (here in Australasia, that’s usually “H1”, which is 7℃ dry-bulb, 6℃ wet-bulb outside and 20℃ inside). But how should the capacity range be interpreted? Is it the available range at those same test conditions? Or is it the minimum and maximum under any (likely different) conditions? Is the “rated” output chosen to maximise the COP or other desirable specification for marketing? It seems manufacturers want you to use the rated capacity when sizing the unit, but I want to be sure that that’s the right way to do it! The old unit was definitely oversized.

(Background: I have a good idea of the 99% Winter design temperature at this site. I’ve measured the heating load on a cold night and determined the thermal resistance of the rooms, and I’m comfortable with how to determine the balance point. I’m aware of the need to derate the heat pump’s output for the design temperature, and I have supplemental heating available and don’t expect that the heat pump will never defrost.)

By: Robin W Boyd

Robin W Boyd — Wed, 24 Aug 2022 14:25:46 +0000

In reply to John Weil. John, I am not aware of any indoor units that do what you are asking. However, there are many variations of indoor units that can be mounted low wall on the floor or ceiling mount depending on physical aspects of the area needing to be conditioned. All of the indoor units take into consideration that the air louvers need to direct the air upward for cooling and downward for heating. A ducted indoor unit can also be installed where we can have the return into the unit up high and duct the supply low on the wall. Pretty much any situation can be resolved with the various indoor unit types.

By: John Weil

John Weil — Thu, 18 Aug 2022 18:01:02 +0000

Thanks Allison and Robin,

Are there any dual-outlet mini-split systems (or any systems) with the Heating mounted or ducted low on the wall and the cooling mounted or ducted up high?

–John Weil

By: Robin W Boyd

Robin W Boyd — Thu, 11 Aug 2022 14:30:36 +0000

In reply to John Weil. I have found that because ductless systems control the evaporator coil temperature to maintain below dewpoint that ductless systems do a good job with dehumidification. When a ductless unit is set to "dry", the evaporator maintains the coil just above freezing by modulating the air volume. This causes the evaporator to use most of its energy changing the state of the water vapor in the air to liquid condensate and less energy removing relative heat from the air. In this way, a ductless unit can dehumidify much better than a conventional split system without overcooling the area.

By: Allison Bailes

Allison Bailes — Wed, 10 Aug 2022 10:48:34 +0000

In reply to John Weil. John: Yes, ductless and ducted mini-splits DO remove moisture from the air. I haven't measured the condensate at my house, but for a while I had the line draining onto the sidewalk in my backyard. It produced a lot more water than I expected, and it did so at times even when I didn't expect to see much.

By: John Weil

John Weil — Wed, 10 Aug 2022 05:41:08 +0000

Maybe this was covered earlier? Do mini-splits actually de-humidify at all. Do the head units have drain lines? Thanks.

By: Shae

Shae — Tue, 19 Jul 2022 12:40:12 +0000

YES!! I agree with the 72 degrees with 40% humidity. I also set my thermostat to 73 and my unit pulls a TON of moisture out no matter what. I also set it down to 70 at night as we like it cold and if its much hotter I wont sleep well.

By: Robin Boyd

Robin Boyd — Sat, 16 Jul 2022 21:51:22 +0000

In reply to Tom Turner. In the Mid-Atlantic region, those rebates and tax credits have caused a lot more harm than good. In order to achieve the ratings for so many cooling systems, they had to utilize oversized gas furnaces. As a manufacturer's rep, I can't count how many oversized gas furnaces had to be replaced after initial installations of oversized furnaces required to meet rebates. So many furnaces were operating more on limit switches than on thermostats.