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Heat pump usage

Woke up this morning on the beautiful Florida Gulf Coast and it was a little chilly - low 50s.  So, I decided to try out the heat pumps which I've never used before.  They worked quite well and warmed up the coach nicely.  But it got me to thinking about how cost effective that decision was.  (I know, we should be out enjoying the morning and I promise that we will be on our bikes shortly).

The evening before I had turned off the hydro-hot (diesel and electric) after our showers.  So, was it more cost effective to  to warm the coach by 1 - turning on the heat pumps, 2 - using the hydro-hot electric or 3 - using the the hydro-hot diesel?

Two other bits of info.  The heat pumps only cycled once to get to the desired temp and then they were turned off as it warms up fairly quickly here.  We are on metered electric so our electric cost is usage based.

Maybe the difference is not worth investigating but I am curious.  Also, what is your preference in this situation?
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Mark & Mary Benko
Former coach: 2005 U295 3823
Jeep Cherokee, Honda Fit

Re: Heat pump usage

Reply #1 –
That is a easy question, since buying electric power is much cheaper than making it. While the diesel fired heater system is very nice, it does cost more than using electric power too.
I have fought this question for years, being in the generator business, I assure you, buying juice is much cheaper than making it.
Cheers
Dave M

Re: Heat pump usage

Reply #2 –
I agree with Dave M as long as the park is not marking up the electric..... also the AH if you were running it for showers would be able t heat up the coach at the same time on diesel so you might try it that way too.
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Heat pump usage

Reply #3 –
Yet another argument for solar panels! :)

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: Heat pump usage

Reply #5 –
Quote from: Steve & Kathy B –
Except for the pay back costs of installation and the parts..  It would take years, but very convenient  :)

The panels are, for right now at least, pretty cheap... right around $1 a watt. Installation can be expensive but you don't actually HAVE to "install" them. I used solar panels by just arranging them around the RV pointed at the sun. In fact, this is probably the most efficient way to utilize them... as long as you rearrange them appropriately as the earth rotates. And "modified sine wave" (heh... I love that term... they're square waves) inverters are also pretty cheap now, too.

So now you just have the panels, an inverter and a regulator and some wire. Under $1k. Not hard to justify when the alternative is running the generator. When you're done just store them away in the "basement".

Of course... if you wanna get fancy.....  :D

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: Heat pump usage

Reply #6 –
Sounds great, But in the real world, running a heat pump / AC from an inverter backed up by solar, the $1 k guesstimate will leave you very cold in winter or hot in summer.
Best Figure on about 4 kw worth or solar panels, about 800 amp worth battery,  great location in daylight and a 2500 watt inverter to even start.
From there just keep driving and stay in the max sun light as long as possible.
Does sound good though.
For me, I will take the power post, generator in summer, and in winter the Aqua Hot or what ever LP Gas does great, but still needs good battery, solar for the DC operation.
Of course this is assuming we are in an area too warm or cold, requiring one or the other.
Just my opinion.

Re: Heat pump usage

Reply #7 –
Going solar does require some compromises, there's no doubt about it. Not as many now as 20 years ago, though. Instead of running the Aqua Hot, maybe a 1kw electric heater would do the trick. And, of course, if you're in Seattle it's going to be problematic anyway. But 600 watts of solar panels will go a long way towards keeping an RV self-sufficient if you're in a reasonable climate.

We lived for 3 years on a sailboat in the tropics using only 60 watts of solar panels and a wind generator.

Craig
1993 U225 36' Unihome GV with PACBRAKE exhaust retarder, Banks Stinger and Solar Panels.
Toad: 1999 Jeep Wrangler 2-door soft-top.

"No one has ever had to evacuate a city because the solar panels broke."

Re: Heat pump usage

Reply #8 –
Ok, thanks guys - I get it - diesel expensive, electric cheaper...  Which leads to a followup.  Is it cheaper to run the 2 AC/heat pumps OR the hydro-hot on electric-only, when it is cool but not cold? 
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Mark & Mary Benko
Former coach: 2005 U295 3823
Jeep Cherokee, Honda Fit

Re: Heat pump usage

Reply #9 –
Mark, I that question too.  My guess....it is cheaper to run the heat pump on electricity fro a few minutes rather than the AH on electricity for a short time if it is only cool outside because the AH does more than heat the interior air for a few minutes.  I will be interested if others think otherwise, but just my guess that you heat more with the AH.  On the other hand, I would guess that we would run the AH anyway to have hot or warm water and pulling a little heat off (with much less noise) would be a good way to go.  Your opinion? 
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Heat pump usage

Reply #10 –
Not a FT owner yet, but I  l-o-v-e  reading this forum...every day.....and I did own a heating/A/C business for many years. 

Heat pumps have what is called a COP or coefficient of performance.  I believe there may be  a new acronym now, but it goes like this:  Good residential heat pumps will have a COP of about 4 ..... meaning that they make heat for 1/4 the cost of simple electrical resistance heating.  As I recall, the COP was referenced to about 50 degrees ambient for an "air over" heat pump using ambient air as the "heat sink".  (Some use groundwater as the heat sink and the COP for those is nothing short of amazing.)  As the outside temp drops, the COP for air-over units drops too.  In residential use, most of the time I would set them up to switch over to simple resistance heat (only) at about 25 degrees outside temp.  Modern day heat pumps (e.g. late 1990s and on) can have COPs of 2 or better all the way down to 0 degrees; i.e., they will still beat electric resistance heating cost-wise by a factor of 2...but as a practical matter, residential heat pumps are never set up to operate in temps that low (the efficiency is still good, but the quantity of heat output at that low of a heat sink temperature won't suffice as the only heat source for a residence.)

Lest. in the name of verbosity,  I get "kicked out of the Foreforum group" let me just state that, on shore power, your RV heat pumps will make heat for much less than your AH in the electric mode......because the AH is, at its roots, a resistance heating device in that mode........ with a big stompin' COP of 1.

Heat pumps can rival/approach natural gas in cost of operation (but NG is still cheaper) and they will, almost certainly, beat propane at current LP costs.  I strongly suspect they will beat diesel also (as in AH in the diesel mode)....but I don't know that for sure.  There may be reasons other than cost of operation to prefer the AH though, I reckon.

Still lusting after a Foretravel in Fairview, TX
Ed S. youracman@yahoo.com




. 



 
Ed Sievers
"Be the person you needed when you were younger"

Re: Heat pump usage

Reply #11 –
You can search the archives for past discussions on this subject.  John Christman did a careful analysis one winter.  It turned out for the electric power costs at my most frequent locations, the diesel price would have to be above $4.50 for electric to win.  Your results may differ.  I use diesel when I'm paying for electric, and electric when someone else is.
Regards,
Brett

'99 42' Foretravel Xtreme
'14 Brown Motorsports Stacker
'05 Chevy SSR
'02 BMW R1150R

Re: Heat pump usage

Reply #12 –
Ed S. -  thanks for the explanation on how the AH electric and heat pumps compare.  Learn something new every day. 
Amos - I searched for John's thread - was this what you were referring to?  Aqua-Hot Fuel Consumption
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Mark & Mary Benko
Former coach: 2005 U295 3823
Jeep Cherokee, Honda Fit

Re: Heat pump usage

Reply #13 –
Mark,

Yes, that's the discussion I remembered.

Brett
Regards,
Brett

'99 42' Foretravel Xtreme
'14 Brown Motorsports Stacker
'05 Chevy SSR
'02 BMW R1150R