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K7JV · 02-07-2020, 07:59 AM

After over 14 years of living almost 50% of the time in our '06 Dynasty, I learned something about our HVAC system. I've heard and read for years that if it gets cold enough outside, our heat pump will transfer over to the AquaHot, automatically. In 14+ years, it had never happened.

Well, two nights ago it got pretty chilly, here in Tucson. We awoke to 23 degrees according to the weather station on our coach roof. SURPRISE (to me!), the thermostat said "HEAT PUMP" and "AUX HEAT" and the AquaHot was doing all that it could do with only the 120 VAC selected. I'd never seen that before. Maybe that's been good planning on our part as to when and where we RV.

Anyway, our heat pump (the front one, at least) is pretty darned effective. When we went to bed the evening before the 23 degree number, I used an IR thermometer to check the temperature at the front ceiling vent and it was indicating air delivery at 106 degrees with an outside air temperature of 30 degrees. I think that is pretty amazing. So I left the thermostat in the heat pump mode and we went to bed. I would love to know at what temperature it switched over to the AquaHot, but we slept thru it. NOTE: That would NOT be the experience if we hadn't been in the dry air of southern Arizona. Humidity in the air changes everything. Had it been more humid, the effectiveness of the heat pump would have been considerably reduced. But I was impressed with the performance of our unit.

By the way, when it gets in the 40's and below, we leave a cube space heater on in the front of the coach. If it's going to get down into the upper 40's, we set it on 750 watts (LOW). If it's going to get down into the low 40's or the 30's, we set it on 1500 watts (HI) and go to bed. So it adds BTU's thru the night and the heat pump does the rest. We very rarely use diesel in a campground or RV park, as it makes us bad neighbors.

I was impressed with the performance and thought I'd share it. And I was impressed that our HVAC control system actually worked as advertised. I was just surprised at how cold it had to be for the changeover to actually take place.

Cheers to all, and happy RV'ing!

96 Wideglide · 02-07-2020, 09:33 AM

Interesting!

I've tested mine, but it's never switched over to AH mode. But then, as we were discussing earlier, you have a different system, with a separate thermostat for your living room zone.

Outbound · 02-07-2020, 04:49 PM

I am amazed your heat pump was putting out 106 degree air with an outdoor temp of 23 degrees with out icing up, makes me wonder if your heat pump has backup electric heat.

96 Wideglide · 02-07-2020, 04:58 PM

Quote:

Originally Posted by Outbound

I am amazed your heat pump was putting out 106 degree air with an outdoor temp of 23 degrees with out icing up, makes me wonder if your heat pump has backup electric heat.

Maybe that's what the 'AUX HEAT' means

.

I've never seen that on my thermostat screen.

Busskipper · 02-07-2020, 05:02 PM

Quote:

Originally Posted by Outbound

I am amazed your heat pump was putting out 106 degree air with an outdoor temp of 23 degrees with out icing up, makes me wonder if your heat pump has backup electric heat.

Very Likely - it was/has electric backup.

Try the same test when it's 40 outside......Will be interesting.

on edit - Good chance the Hydro Hot came on because the Basement demanded heat to keep from Freezing? .. as the electric Aux Heat was doing 106.

JohnBoyToo · 02-07-2020, 05:06 PM

Aux heat IS a heat strip - makes the electric meter spin like a helicopter blade

I don;t even try heat pump if it's going below 45, they are loud and inefficient - just set the furnaces to the temp we want and let if work like it was intended.

jcussen · 02-07-2020, 05:44 PM

My coach will go to aqua-hot when heat pump cannot maintain temps, Not sure what causes it, probably outside ambient temps, or, defrost mode. Never seen a roof ac/heatpump that also has a heat strip. Roof heatpump is 12000 btu's and heat strip is 5100 btu's, so if it gets too cold for heatpump operation, doubt the heat strip will do much.
Heat pumps are the most effective mode of rv electric heating, but do not compare with diesel or propane heating for efficiency.

HJLowell · 02-07-2020, 07:09 PM

Mine switches at about 30- degrees.
Im glad I alway keep the diesel burner switch on.
We woke up to outside temps of 15 degrees.
We were warm and toasty inside.

HR2004 · 02-07-2020, 07:50 PM

We are also in Tucson at Justins Diamond J rv park and the other night our rear heat pump which is 2 years old on our 04 HR kicked over to the furnace at 33 degrees.. was makeing some heat to that point but I didn't get out my temp tool to check how much heat it was making before it switched.. we also have a space heater on low up front.

K7JV · 02-07-2020, 07:58 PM

I wish it could. It was putting out the 106 degree air the night before, before we went to bed. The OAT at that time was 30 degrees. I was still pretty amazed it was doing that well at 30 degrees. No, our system doesn't have any auxiliary heat strips within it.

K7JV · 02-07-2020, 07:59 PM

I never had, either, Ben. I don't remember AUX HEAT even being mentioned in the thermostat documentation. But that morning, it was there.

jcussen · 02-07-2020, 08:15 PM

Thinking humidity has a lot to do with it. Down here by the coast you can have 70% humidity at 45 f. So ice can build up on condenser coils when on heat pump mode, and cause defrost mode, or switch to furnace mode, but in the desert with low humidity, heat pump can probably operate to much lower temps.

96 Wideglide · 02-07-2020, 10:10 PM

Quote:

Originally Posted by K7JV

I never had, either, Ben. I don't remember AUX HEAT even being mentioned in the thermostat documentation. But that morning, it was there.

I may just have to run my test longer. Someone mentioned it may depend on how often the HP has to defrost.
Good to hear your's works properly

!

K7JV · 02-08-2020, 07:37 AM

Please know that I was just sharing my experience, and my pleasure that things actually worked as designed, even after 14 years of enjoying it.

The only reason it went so far beyond normal expectations is that the Tucson air was really dry. Ben is right. Humidity changes everything. And I didn't say anything about economy.

The more moisture there is in the air, the more condensation will form on the evaporator, an d in lower temperature, freeze. As a result, the moister and the colder it is outside, the more the unit will have to defrost. When that happens, the amount of heat energy delivered to the coach is reduced due to the "down time" while the unit defrosts. The unit is less able to keep up with the heat loss in the coach, hence alternative heat may be required. The compressor keeps running during the defrost cycle, so the overall electrical energy efficiency begins to drop, significantly.

I was fortunate! The environmental conditions were right a few nights/mornings ago, and my fourteen-year-old front heat pump simply exceeded all of my expectations, and the fact that it changed over to the AquaHot on its own for the first time EVER, really pleased me. Everything worked as advertised. Yay! ��

Cheers to all!