Heat pump happiness

We have heard other RV’ers talk about boondocking (living without hookups) and say, “it’s great, but don’t expect to run your air conditioner.”  Some of these folks know a lot about solar and batteries and living off-grid.  I’m happy to report that we are having a different experience.  We have been off-grid since early April (without propane or a generator) and we stayed cool all summer with our heat pump air conditioner.  We’ve been parked in full sun and 100-degree heat, completely comfortable inside Howie.  Now that it is getting cooler, we are using the heater and enjoying that too.

It might be a specific case – we have a lot of roof space for solar panels, we installed a large battery bank, we have a small trailer that is easy to cool down/warm up, and we have not thoroughly tested various temperature/humidity combinations.  We might end up plugged into external power during the winter in order to have enough energy for heating (with colder, shorter days and likely more clouds for less solar charging).  We just started this experiment in May and we don’t know how reliable our setup will be.

On the other hand, we aren’t toughing it out nor sweating half the day.  Whenever it starts to feel warm inside, the AC goes on (at a minimum on the Dry setting) and we’re comfortable.  We routinely turn it on just to use some energy so we aren’t “wasting” what is coming from the solar panels.

Honestly, it’s pretty amazing.  I’ll try not to go on and on!  Just know – there is a “heat pump happy dance” now.

The heat pump

What is a heat pump?

From the Trane website:

“Technically, a heat pump is a mechanical-compression cycle refrigeration system that can be reversed to either heat or cool a controlled space.  Think of a heat pump as a heat transporter constantly moving warm air from one place to another, to where it’s needed or not needed, depending on the season.  Even in air that seems too cold, heat energy is present.  When it’s cold outside, a heat pump extracts what outside heat is available and transfers it inside.  When it’s warm outside, it reverses directions and acts like an air conditioner, removing heat from your home.

“A heat pump consists of two main components: an indoor air handler and an outdoor unit similar to a central air conditioner, but referred to as a heat pump.  The outdoor unit contains a compressor that circulates refrigerant that absorbs and releases heat as it travels between the indoor and outdoor units.”

(Side note that I can’t help but smile over the word “transporter”)

Basically, a heat pump is an air conditioner AND a heater.  It’s just as efficient as an air conditioner and more efficient than a heater that burns fuel to create heat.

We bought a ductless version called a mini-split.  Compared to our old air conditioner it is much quieter.  Even more so compared to our old heater which had ducts running different places.  We barely hear it when it’s on.

Apparently buildings can use a central heat pump plus ducts to move air around (like central air conditioning).  The difference with a mini-split system is that there are no air ducts (the refrigerant goes to individual rooms instead), and you can have registers in different rooms to control the temperature separately by register.

For the purposes of this post, I’m going to use the terms “heat pump” and “mini-split” interchangeably, hopefully that’s not too confusing.  Just trying to figure out how to write the previous 2 paragraphs was confusing to me, but maybe a drawing will help.

This is a simple mini-split diagram of the flow of air (thicker arrows) and refrigerant (thinner arrows), although our particular system has only one indoor unit:

We bought a 9000 BTU heat pump made by Pioneer.  The SEER (Seasonal Energy Efficiency Ratio) rating is 19.5.  It uses 120V AC power, so the inverter needs to be on for it to run.

Model Number: WYS009AMFI19RL-16

The spec sheet (in 3 parts) for further details:

This is the smallest mini-split we could locate, knowing we didn’t have much interior space to cool/heat.  We had it shipped to us but I believe there are similar options at hardware stores.  There are also HVAC companies that will install it in your home, although I don’t know how they would react if you asked them to put one in your travel trailer or RV.

Installation

Choosing the heat pump was easy.  Installing it in a travel trailer was not nearly as straightforward.  Luckily John was willing and able to figure it out.  Huge thank you to John!

He might have developed this idea in the first place when he looked at the trailer tongue, now free of propane tanks and batteries, and wondered what could sit there.  He might eventually get a toolbox, but when the heat pump was suggested I immediately jumped on that instead.  An actual air conditioner?  A more efficient heater?  Um, yes please, let’s do that!

We had removed our roof air conditioner because we rarely used it, it was old and loud and inefficient, and it added some extra inches to the trailer height that seemed unnecessary.  Plus without the roof AC unit, we have more room for solar panels.  I figured I could continue with the “heat acclimation” concept and just plan not to be anywhere too hot for too long.

But a heat pump, that is a worthwhile experiment.  All in the name of more data collection!

The external unit of the heat pump sits on the tongue.  John added a couple Unistrut mounting bars, and it seems to be riding well.  It has tagged along with us from Texas to Arizona to California to Wyoming to Utah.  So far, so good!

I do suspect we have voided the warranty by doing this, but we’re OK with that.

One thing that had to change was our hitch equalizer (weight distribution) system because the lever tensioners were in the way.  John found another design that hangs below the hitch, and looks to be an improvement anyway.  This added some cost and effort, but also resulted in an upgrade to our tow system.

Hooked up for travel:

The indoor unit (also called a register) fits inside a kitchen cabinet, or what used to be a cabinet.  John removed the doors and I removed most of the contents.  It’s a good location because the air blows straight back through the whole trailer, plus it’s as close to the hitch as it could be.

Another photo after John covered the lines on the left side.  The heater is running in this picture.  It’s nice that there is still space under the register for a few items.

John figured out a way to run lines from the inside unit to the outside one.  He snaked everything through holes straight down through the floor and looped them up toward the outer unit.  You can buy longer refrigerant lines if the inner and outer units are further apart; in our case, 10 feet was barely long enough.

In addition to the refrigerant lines, John ran AC power and controller lines between the inside and outside units.

He then spent time leak-checking the system.  He’d purchased a vacuum pump and some cheap HVAC gauges.  When he initially pulled a vacuum on the system, it didn’t hold.  It turned out that the leak was most likely in the gauge hose connection, which he figured out after redoing each end of the refrigerant lines to the heat pump.

Once he fixed the gauge connections, he pulled a vacuum and then “released the hounds!”, I mean “released the refrigerant!”  No leaks, and everything is looking good so far.

In case anyone is thinking of doing something similar (and I highly recommend replacing whatever you have with a heat pump system), John suggests that getting a professional HVAC person involved could be a good idea.  Their professional set of tools alone would be helpful.  He looked into this for our installation, but the quoted cost was more than we paid for the heat pump itself.

What it does

The mini-split has several modes:
– Cool, for air conditioning
– Heat, for heating
– Dry, for dehumidifying
– Fan, for moving air

Cooling has an operational range of 32° to 122° F (outdoor temperature) and 63° to 90° F (indoor)

The heating range is 5° to 86° F (outdoor) and 32° to 86° F (indoor)

Dry mode works best at 32° to 122° F (outdoor temperature) and 50° to 90° F (indoor)

If the temperature is outside the “operational range”, according to the manual the unit will perform less than optimally.  Pioneer sells an Arctic version (including an electric heater on the outdoor unit) that will work fine at outdoor temperatures as low as -12° F.

We have tried all of the modes and I’m now officially spoiled for climate control.  I don’t yet have a lot of data, mostly some qualitative remarks along with an intention to run actual data collection tests for a future post.

Dry – works amazingly well in humid conditions.  It feels like air conditioning and I think uses less energy compared to Cool mode.  I didn’t collect any power usage numbers while we were in Texas, and we haven’t felt one drop of humidity on our travels in the west, but eventually I’d like to compare Dry to Cool for effectiveness and power draw.

Cool – very quickly drops the temperature inside our trailer, even when it’s 100 degrees outside.  It’s efficient, and it generally doesn’t take long before the power draw drops below the amount of incoming solar (as long as there is sunshine on the panels).  In other words, we are frequently running the AC at the same time that the batteries are being charged.

Heat – we love to turn it on first-thing on chilly mornings to make it much easier to get out of bed.  So far we haven’t experienced below-freezing temperatures, mostly down in the low 40’s.  Mornings with the heater on are comfortable and we aren’t running the batteries down too far before the sun starts recharging them again.

The one thing the heat pump doesn’t do is heat the floor (did someone say… radiant heating?), so we still wear rubber sandals in the house and I use my heated footrest on colder days.

I do have a little bit of data.  This comes from watching the wattage numbers on the battery meter (when there is no incoming solar).  I would love to find a way to graph this or collect cumulative numbers specific to the heat pump, but don’t know how to do that yet.  We don’t have a standard AC plug that I can connect the Kill-A-Watt to.

1) 77° F outside, full sun, 72° F “Cool” setpoint:
– I turned on the air conditioner; power draw = 860 watts
– It ramped up to 1000 W in the early stages of cooling, then dropped to zero after about 15 minutes
– The wattage numbers ranged from 0, 130, 250, 430, to 670 watts (up and down) for the next couple hours in order to control the temperature

I should have repeated the AC test when it was actually hot outside (Moab in August), but didn’t think to do so.  Qualitatively, energy usage is not much higher compared test #1 even when it is very hot outside.  I also need to include the indoor temperature since we now have the thermometers for that.  Future experiment!

2) 42° F outside, no sun (before dawn), 78° F “Heat” setpoint:
– I turned on the heater; power draw = 150 watts as it was getting warmed up (before the fans turned on)
– It ramped up as it heated up and started blowing warm air, up to 800-1100 watts
– Soon the power level dropped down and stayed between 300-500 watts all morning
– This brought the inside temperature up from 55° eventually to 70° F , as the outdoors also warmed up over a few hours

There is a “Follow Me” mode on the remote, which uses the temperature sensor on the remote instead of the one at the register.  The temperature at the register can change pretty quickly, while the rest of the house takes longer to warm up (or cool down).  In our case especially, the register is in a small space and enclosed on 4 sides, so the air around it heats (or cools) right away.

I did a follow-up “Follow Me” test, with quite different results in levels of heating and energy usage:

3) 43° F outside, 53° F inside, no sun (before dawn), 70° F “Heat” setpoint, “Follow Me” turned on with the remote sitting on the table about 10 feet from the register:
– Similar startup and warm-up power draw, from 200 watts slowly going up to 1400 watts in about 10 minutes (a bit higher on the top end this time)
– The power readings then dropped to 900 to 1100 watts and stayed there for about an hour as the temperature at the remote increased from 53° F to 63° F
– Over the next hour there was a slight drop in power, to around 700 to 900 watts while the temperature increased another 5° F (close to the setpoint)
– I stopped the test at that point because everything was warmed up nicely
– Total battery usage was about 2.2 kWh over 2.5 hours; significantly higher than test #2, but our house also warmed up significantly faster

So just be aware of the difference it can make to activate “Follow Me”.  On our system, the setting turns off every time we turn off the heat pump, so it defaults to “Off”.

4) “Fan” mode: Power draw is less than 10 watts at all fan speeds (basically negligible)

Functions

The programming is reasonably versatile, with the following functions available:
– Mode (auto, cool, dry, heat, fan)
– Eco (energy efficiency) air conditioning
– Vacation (freeze protection) mode, which we might use overnight in the winter
– Timer for delayed on or off
– “Follow me” mode to use the temperature sensor on the remote to control the unit
– Turbo to reach the temperature setting as quickly as possible
– Swing and direct to auto-swing the louver and set the air direction
– Self-clean

Home improvements

Not specifically related to the mini-split, but we needed to move some things out of the cabinet over the sink to make room for the indoor register.  We have the ability to reorganize because there is no longer a propane stovetop, nor propane ductwork under the counter.  So much extra space!  I’m gradually rearranging the contents of the kitchen as John creates new opportunities.

Here’s where the propane stovetop used to be, with the beginnings of a new drawer:

Either a new yoga pose or John is hard at work (or quite honestly, he might be taking a nap):

Sometimes we have a pile of stuff in the middle of the trailer:

But eventually something new comes out of it:

There is also space available where the propane ductwork used to be, so John added a fourth drawer below the original three.

There is now a “hidden” shelf under the corner of the countertop, because John couldn’t stand to let that space go to waste.  It’s a bit hard to access (or photograph), but a good place to put paper products:

John is working toward a more permanent countertop (project pending); here is the one that is temporarily in place.  More counter space, yay!

Summary

We love everything about the new heat pump.  It’s super quiet, efficient, fast, safer, and perfect for our space.  Removing all propane-powered appliances and replacing them with electric versions has worked even better than we expected.