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Comment by aga98mtl | Hacker News Reader

In my part of Canada it is common to have mini-split (non-ducted) heat pumps, mainly for cooling. The salespeople like to say that you will save a lot on heating with a COP of 3. However the placement of the inside unit is always close to the ceiling, usually in the highest part of the house. This is perfect for cooling during summer. However during winter, it causes the upper part of the house to be hot and the floors to be cold. The basement resistive heaters have to compensate to maintain the target temperature. This means that these single head mini-split heat pumps cannot replace 100% of your heating and cannot provide the same level of comfort than resistive baseboards.

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What you say is true, though another approach that could be more efficient is to simply run the heat pumps with a higher setpoint rather than supplementing them with [as much] resistive heat (especially in the majority of season that isn't the coldest design day).

It might "feel wrong" to set the heat pumps to 25°C, but that could easily be cheaper and more efficient than setting them to 20-21°C and supplementing to the same level of comfort with CoP of 1 resistive heating all season long.

I have the same setup as GP and setting a higher temp doesn't help at all. My thermopump is in the main hallway on the second floor and blows towards the master and second bedroom, above the stairs. In summer it's great because it sends cold air everywhere and lets it sink to first floor. In winter, it just creates an insufferable hot bubble on the second floor. I already prefer to sleep in the cold and just use baseboard heaters on the main floor and bathroom. I don't even heat my bedroom.

Sounds like a ceiling fan or some sort of air circulator is in order. If you put a ceiling fan on blow to push the hot air down it will blend with the air in the rest of your house and improve the overall comfort of your space.

If that won't work, for instance your home is very boxy and separated, it might be worth looking into AC duct boosters on the far away areas to suck more air out of the ducts from farther away.

If I misunderstood and you have a ductless system, they make electric fans that go in between paired walls and look like a ducted register, but that are very useful for blending air between two rooms. A few of those alongside a through floor to ceiling below fan duct might be available that could help even out temps in your house even more.

Do heat pumps not just work in an "on/off" fashion that shut off when the thermostat say "ok, that's enough"? I know that modern forced air natural gas furnaces are a little smarter and will have stages to balance for noise, but they are really just "on" or "off", pushing much hotter than ambient air around until the rooms settle to the desired temperature.

Most heat pumps now are variable speed/output. I suspect all low-outside temp capable heat pumps are variable speed/inverter drive.

Is the speed/output a high/medium/low type deal or a specific temperature?

The outdoor unit can vary the frequency of the compressor drive to track a desired refrigerant temperature in the face of varying load from the indoor unit. As the indoor air comes closer to the desired temperature, it will cool off the returning refrigerant less than when there is a large delta-T. The outdoor unit can adjust the compressor speed to closely match the heat transfer and run continuously at a lower speed rather than cycling on/off. There is a minimum speed below which the compressor can't run [and so would have to cycle], but in general the outside unit is smoothly variable.

The indoor unit fan speeds are only loosely connected to this. (The higher the indoor fan speed, the greater the heat transfer and load on the compressor, all else being equal.)

My part of New Mexico (6000'/2000m) may not get as cold as your part of Canada, but I simply have not found what you claim to be true.

My house has several "lifted ceilings" (15'/5m) and it is true that the heat from my minisplit units wants to accumulate up there. In some rooms we have ceiling fans that help move the air down (or up). In other rooms, there are no fans, and the upper part of the room space is indeed way, way hotter than the lower part, which is ridiculously inefficient.

HOWEVER ... this has never impacted the ability of the minisplit units to provide more than the same level of comfort as floor-mounted heating devices.

My tips would be: (sorry if they are a bit obvious)

1. Make sure to point the vents down so the hot air blows into the lower area. (And naturally, in the summer when you use them for cooling they should point up)

2. Set a higher temperature. The thermometer tends to be part of the unit itself so it tends to measure the hottest spot in the room (both when heating and when cooling), so you think you are wasting money blasting the heat to 25C when actually it is just that the unit isn't running since it only keeps itself hot. Some units come with a function that pretends to use a thermometer built into the remote, but I don't think I've ever seen it do anything other than burn through the batteries.

3. Since you are talking about mini-split heat pumps (plural) I assume you have one per room so a good tip here would be to close the door to that room.

For my own needs they are more than enough, but then again it doesn't get quite as cold in Israel as it does in Canada :)

Heat pumps don't have to be air-air pumps. Most commonly these days I hear people installing air-water heat pumps to replace gas furnaces that heat water for radiators or under-floor heating. For new houses around here, ground-water heat pumps are actually most common as they are very efficient even if it's cold outside, but they require diffing up a large area to install the under-ground piping.

My wife’s uncle has large pond outside his house and wedding venue. He has two units. One closed and one that directly draws the water. The closed unit has half a mile of coils sunk in the pond. He says the open unit is more maintenance.

His heating and cooling bills are not far off from my house. Considering he has 3 buildings similar sized to my house it’s a pretty drastic reduction.

Yeah, there are of course also water-air, water-water pumps (although I've never heard of the open-circuit ones, but yeah, why not). But you have to have access to a large enough body of water that doesn't freeze and has enough capacity.

The main issue for me with air-X heat pumps is that over time it can start to make a lot of noise if not well maintained.

But the closed-circuit under-ground (or under-water) ones essentially don't need maintenance and are incredibly efficient, as the source never goes very cold.

This is one of the critical problems for heat pumps being a silver bullet for climates that are both hot and cold. You buy them for AC but they dont work for heating due to the physical location or alternatively you need another heat pump that is cost ineffective. That and it gets quite expensive to heat in cold weather.

To get rebates in NS need to put a head per level. Also the systems can typically work a temperature sensor that's not in the unit. It can be in the remote or in a wired thermostat. This avoids the unit shutting off because the ceiling is hot.

Mini splits don't have to be installed high up on a wall, indoor handlers come in a variety of form factors, you can get thin "console" units that are floor mounted against the wall.

Put circulator fan to mitigate

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