Should we put in AC

[GordMay]

Originally Posted by s/v Jedi

The savings are 50-60% and it’s whisper quiet and without startup surge.

Mabru claims “Super high efficiency by design”, but, I didn’t see any SEER* ratings.
➥ https://mabrustore.com/collections/mps-dc-units

What 'magic' could possibly make their units so much more efficient?
Variable fan & compressor speed technology, for instance, only provides energy [& noise] reductions/savings, when the demand is significantly lower than “normal”, and the unit is running at much less than capacity.

*The efficiency of an HVAC system is determined by its Seasonal Energy Efficiency Ratio, or SEER.

[s/v Jedi]

Originally Posted by GordMay

Mabru claims “Super high efficiency by design”, but, I didn’t see any SEER* ratings.
➥ https://mabrustore.com/collections/mps-dc-units

What 'magic' could possibly make their units so much more efficient?
Variable fan & compressor speed technology, for instance, only provides energy [& noise] reductions/savings, when the demand is significantly lower than “normal”, and the unit is running at much less than capacity.

*The efficiency of an HVAC system is determined by its Seasonal Energy Efficiency Ratio, or SEER.

When the compressor runs at a lower speed, it is much more efficient than at maximum speed, especially when it leads to short cycling. The new units try not to cycle at all or at such low speeds that you don’t even hear the compressor start.
There have been many reports by owners, here on the forum, confirming these savings as they run their A/C all night from inverter.

[GordMay]

Originally Posted by s/v Jedi

When the compressor runs at a lower speed, it is much more efficient than at maximum speed,...

So, as I said, there’s no significant savings, when the A/C is running at/near full load - when you really need it.
The savings come into play, when the A/C faces much reduced cooling demand - when you may not really need it.

Are you aware of their SEER ratings? [I didn't see them - a red flag, to me]

Don't get me wrong: I think it's a great technology; but, perhaps, a little over-stated, in this case.

[s/v Jedi]

Originally Posted by GordMay

So, as I said, there’s no significant savings, when the A/C is running at/near full load - when you really need it.
The savings come into play, when the A/C faces much reduced cooling demand - when you may not really need it.

Are you aware of their SEER ratings? [I didn't see them - a red flag, to me]

Don't get me wrong: I think it's a great technology; but, perhaps, a little over-stated, in this case.

But that isn’t how it works. At full load a traditional system must be at a 50% duty cycle, i.e. only run half the time. They are not engineered to run 100% duty cycle.

[GordMay]

Originally Posted by s/v Jedi

But that isn’t how it works. At full load a traditional system must be at a 50% duty cycle, i.e. only run half the time. They are not engineered to run 100% duty cycle.

Modern air conditioning units are designed to run continuously, 24/7.
In fact, air conditioners should be sized to run almost continuously, at the design temperature.
Your location will go above the design temperature only 1 - 2% of the hours in a year, based on a 30-year average.
Under moderate conditions, the compressor may run about 70% of the time, roughly 16 hours out of 24.
Extremely high outdoor temperatures can increase the compressor’s runtime to 90-100%.
So, for about 88 - 175 hours a year, I would expect a properly sized air conditioner to run continuously.

So, no, it does not put any undue strain on the air conditioner to run continuously.
However, all mechanical things have a certain amount of hours they can work, before they break.
Where I am, it is a mild [cooling] climate, and not at all uncommon to see 30 year old air conditioners.
In an extremely hot climate, 10 years is getting pretty old.

[SV Confianza]

Originally Posted by s/v Jedi

The savings are 50-60% and it’s whisper quiet and without startup surge.

How was that measured or estimated?

[Mickeyrouse]

The thing about air conditioning on boats that always puzzles me is….sailing is an outdoor activity. Yes we have A/C that we run in the evenings when we’re at a dock, and appreciate it. But we don’t normally try to sail dock-to-dock. Our most enjoyable times on boats (we’ve been doing this long enough to have grandkids that sail with us) have been on the hook. If I need to spend my time indoors with the A/C I might as well be at home where the furniture is more comfortable, the ice is more plentiful, the day more routine, and the scenery more predictable.

[s/v Jedi]

Originally Posted by GordMay

Modern air conditioning units are designed to run continuously, 24/7.
In fact, air conditioners should be sized to run almost continuously, at the design temperature.
Your location will go above the design temperature only 1 - 2% of the hours in a year, based on a 30-year average.
Under moderate conditions, the compressor may run about 70% of the time, roughly 16 hours out of 24.
Extremely high outdoor temperatures can increase the compressor’s runtime to 90-100%.
So, for about 88 - 175 hours a year, I would expect a properly sized air conditioner to run continuously.

So, no, it does not put any undue strain on the air conditioner to run continuously.
However, all mechanical things have a certain amount of hours they can work, before they break.
Where I am, it is a mild [cooling] climate, and not at all uncommon to see 30 year old air conditioners.
In an extremely hot climate, 10 years is getting pretty old.

No they are turned on continuously but are designed for a 50% duty cycle.

[SV Confianza]

Originally Posted by s/v Jedi

When the compressor runs at a lower speed, it is much more efficient than at maximum speed, especially when it leads to short cycling. The new units try not to cycle at all or at such low speeds that you don’t even hear the compressor start.
There have been many reports by owners, here on the forum, confirming these savings as they run their A/C all night from inverter.

I can't find any corroboration of this claim. How does it run more efficiently at slower speeds and by how much? If this was true, in the case that the A/C is not at max capacity, it would indeed provide energy savings throughout the day.

They key would be that it would have to actually run more efficiently at lower speeds.

I can't find anything that corroborates it. I see lots of misquoting and misunderstanding of some Gambica "study" / marketing content that says a 20% reduction in speed gives a 50% savings in energy. 1. that's in a certain type of application, and two, it assumes there would then be a 1:1 relationship for speed to cooling (which we should be looking at Work to cooling or energy to cooling).

[SV Confianza]

Originally Posted by s/v Jedi

When the compressor runs at a lower speed, it is much more efficient than at maximum speed, especially when it leads to short cycling. The new units try not to cycle at all or at such low speeds that you don’t even hear the compressor start.
There have been many reports by owners, here on the forum, confirming these savings as they run their A/C all night from inverter.

I run my traditional A/C all night from the inverter too. And I can't find anyone doing actual power comparisons from their old unit to a new VSD.

It just doesn't make any sense. The compressor is still a compressor. It has the same efficiency as a traditional one. VSD alters the speed, while traditional cycles. Sure, you'll save the power from the startup inrush from the cycling I guess?

[s/v Jedi]

Originally Posted by SV Confianza

I run my traditional A/C all night from the inverter too. And I can't find anyone doing actual power comparisons from their old unit to a new VSD.

It just doesn't make any sense. The compressor is still a compressor. It has the same efficiency as a traditional one. VSD alters the speed, while traditional cycles. Sure, you'll save the power from the startup inrush from the cycling I guess?

It’s fine, you don’t have to believe me and I have no interest in convincing you, so I recommend you search the forum for the reports I mentioned. Maybe those members will even chime in to your questions

[s/v Jedi]

Here is a good example, from Thermodinamica. A 16,000 btu unit, afaik normally uses 1.8kW while their unit only uses 0.8kW and that is including the seawater pump.

That’s more than 50% power savings.

[SV Confianza]

Originally Posted by s/v Jedi

Here is a good example, from Thermodinamica. A 16,000 btu unit, afaik normally uses 1.8kW while their unit only uses 0.8kW and that is including the seawater pump.

That’s more than 50% power savings.

The popular 16k btus are around 1.2kW. Not a 50% reduction, but still .4kW reduction is pretty good.

Edit, just read their documentation. It's 0.95kW for the unit. They're bullshitting a bit advertising .8 until you get into the details. So it's .25kW (21%) saving for triple the cost. I guess that could be worth it depending on the situation.

[s/v Jedi]

Originally Posted by SV Confianza

The popular 16k btus are around 1.2kW. Not a 50% reduction, but still .4kW reduction is pretty good.

Edit, just read their documentation. It's 0.95kW for the unit. They're bullshitting a bit advertising .8 until you get into the details. So it's .25kW (21%) saving for triple the cost. I guess that could be worth it depending on the situation.

My CruiseAir 16,000btu unit takes 1,800W.

[SV Confianza]

Originally Posted by s/v Jedi

My CruiseAir 16,000btu unit takes 1,800W.

That's...a lot. When we looked at options, we considered these (from the traditional, non vsd type) and pitted their stats agains the VSDs

Webasto FCF Platinum - 16k btu - 1288W
Dometic Marine Air EnviroComfort 16000 - 1208W
Marinaire MSBA16k2 - 16k btu - 1242W