Advice on replacing both rooftop ACs with heat pumps

Topic: Advice on replacing both rooftop ACs with heat pumps (Read 3746 times) previous topic - next topic

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #25 – July 24, 2018, 07:15:07 am

Thanks for your interest. I will make a video showing:

- Decibel readings, old Penguin 1 units, various locations
- Decibel readings, new Brisk II Air units, various locations
- Hook up of CC II thermostat
- High and low air flow settings
- Heat pump settings and Decibel readings

I just downloaded the top-rated IOS app for Decibel measurement, called SPLnFFT. Funny name, but it works great.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #26 – July 24, 2018, 03:40:54 pm

I think your the 99 has heat strips not heat pumps.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #27 – July 24, 2018, 06:52:09 pm

The old ACs have heat strips. The new Brisk II Air units I ordered have heat pumps, not heat strips. It was about $150 each more expensive , but they will be much more energy efficient than heat strips. Yes, heating will cause more wear on the compressor, but I heard that it is good to run the compressor monthly, like the generator, to keep the lubricant circulating.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #28 – July 24, 2018, 07:03:17 pm

Quote from: Tim – July 24, 2018, 06:52:09 pm

The old ACs have heat strips. The new Brisk II Air units I ordered have heat pumps, not heat strips. It was about $150 each more expensive , but they will be much more energy efficient than heat strips. Yes, heating will cause more wear on the compressor, but I heard that it is good to run the compressor monthly, like the generator, to keep the lubricant circulating.

Heat strips are about 5100 btu's max. Heat pump is about 12100 btu's for the same 14 amp draw. Well worth the extra money if you have to pay for your electricity. Heat pumps only good down to 45 f. or so but heat strips at 45 f. don't do too much and you will probably need your furnace anyway.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #29 – July 24, 2018, 10:51:00 pm

My guru buddy mentioned greatly decreased service life on heat pump a/c's.

Foretravels basic design was to have ultimate backups.

If the aqua hot or the propane furnaces die and the weather is below 40 degrees you will freeze witg heat pumps. Period.

I have used a/c heat strips at -30F. Straight manual control on the old Coleman roof airs. Separate from the house furnaces.

Appreciated at that temp that both systems worked at the same time.

Days long ago when rving was an adventure. Single pane windows. Mylar window roll up shades. Lined velvet draw drapes.

Fluorescent bulbs behind the valances. Wooden under cabinet lights. Three panel sliding side body windows. Opening center.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #30 – July 24, 2018, 11:19:47 pm

Have had 3 different coaches with original ac/heat pumps that were 15 to 20 years old. Did have to change out two reversing valve coils [$10 each]. Heat pump operation is the same as ac operation except reversed, so wear is the same either way you use it. In Texas we use air con. 8 months a year, and heat pumps 4 months a year.
If someone can stay warm at -30 F on only heat strips, they are a lot tougher than I am. Heat pumps are noisier [but about the same as ac mode] but at over twice the efficiency, worth it to me, unless at a campground where electricity is included, in which case I will use my little cube heaters or aqua-hot on electric.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #31 – July 24, 2018, 11:32:28 pm

Not heat strips only, both the strips and furnaces were necessary and a hair dryer to defog the windshield as little hot water came to the dash at minus 20 at 3am

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #32 – July 25, 2018, 12:04:53 am

Easy to extend gutter so gutter ac water drains more forward so it is not on awning & step. Also add plastic gutter extenders so water drains to ground without usually touching coach.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #33 – July 25, 2018, 01:16:33 am

My furnaces ductwork is grossly undersized, my
older propane furnacea would only run about 8 minutes before the high limit switch would shut off the burner even at 15 degrees outside and 50 degrees in the coach. This sets up a viscous cycle as the discharge air temp would climb to 190 with horrible efficiency shut off burner but continue to run the fans bringing in cold air into the heat exchanger and cooling the coach. Coach furnace size was probably based on old RIVA standards or a rule of thumb bullshit number based on very little insulation and heating up a travel trailer in 30 minutes. Our coaches have decent insulation. New two stage rv furnaces are no help as it's only available on the 35 mbh model. If you want consistent, comfortable, efficient, and quieter heat consider downsizing the unit. I will be moving the smaller bedroom unit to the front of my coach and getting a smaller unit for the rear. Your worst case scenario should be 100% furnace run time in extreme conditions with the coach being a degree or two below your normal confort level.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #34 – July 25, 2018, 07:12:11 am

Would this group recommend that I add heat strips, to give more flexibility on heating? I believe most home heat pumps have heat strips for when low temperatures make heat pumps inefficient, or even harmful to the compressor.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #35 – July 25, 2018, 08:29:12 am

We've lived almost 40 years in our house in TX with a heat pump + resistance heat strips as our cooling and heating source. Has always done the job just fine with our relatively mild temps. Down to 40 degres, we leave the system in AUTO and it cools/heats as necessary. Below 40 degrees or in sleet/snow conditions, I switch to the AUX heat setting, which uses the heat strips + indoor air handler to circulate the air, but shuts off the outside compressor unit. The heat strips probably draw a lot of power, but I think cutting off the outside (dual) compressor unit saves power, so overall pretty much a wash in terms of power usage.

Our coach still has the original Penguin units which (I think) are not heat pumps, but do have heat strips. They can be used as heaters much the same as our house system, since the compressor (I think) does not run in HEAT mode, but the fan motor does. However, we don't like listening to the roof unit fans running all the time, so we choose to not use them as heaters.

Instead, we prefer using several small electric space heaters scattered around the coach to provide (relatively) quiet heat where we need it. If they are insufficient, then the original propane space heaters come on to take up the slack. If we are dry camping, of course, the propane heaters do all our heating. This works for us, but we normally only camp in fairly mild conditions so we never see really challenging COLD temps.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #36 – July 25, 2018, 08:31:39 am

Tim,
I would add the heat strips.
A lot of parks charge more for a 50A site.
I would run the front unit on electric heat all night and set both thermostats at 60 for the night. Comfortable up front in the morning.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #37 – July 25, 2018, 09:38:29 am

Phred I am very interested in your results when you upgrade the heating system on your ORED. The design turns on the fan first in case of a gas leak then the flame then when it reaches its temp setting the flame cuts off and the fan stays on till the furnace cools off.

Not sure any resizing would alter that particular feature. The short cycling is annoying although.

In ultra cold weather the furnace's btu seemed to be closer to correct. Obviously not optimal for normal cool conditions

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #38 – July 25, 2018, 09:39:08 am

Quote from: Tim – July 25, 2018, 07:12:11 am

Would this group recommend that I add heat strips, to give more flexibility on heating? I believe most home heat pumps have heat strips for when low temperatures make heat pumps inefficient, or even harmful to the compressor.

Have never seen a rv ac/heat pump with heat strips as well, if you do find one, you will need to do some thermostat modifications to handle the extra element. Why don't you just get the ac/heat pump and a couple of walmart cube heaters for when it is too cold for the heat pump? The penguin 2 has a circuit that prevents operation when too cold so you cannot damage the compressor.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #39 – July 25, 2018, 12:30:32 pm

A few questions:

1. Don't most home heat pumps have heat strips that automatically engage below freezing?

2. Why don't most RVs have this feature?

3. The Dometic Brisk II Air may have a feature which turns on the furnace, or am I reading the manual wrong?
Here is an excerpt:

"If system includes a gas furnace, route two 18 gauge thermostat wires from the furnace to the roof opening of the unit that will control it. If more than one furnace is to be used, route the second set of thermostat wires to the second unit."

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #40 – July 25, 2018, 12:36:42 pm

Attached are the dip switch settings, which include:

Heat strip
Heat pump
Furnace / Aquahot

It's not clear if:

1. Can both heat pump and heat strip can be set?
2. Can the logic in the control module handle turning on a heat strip or fuirnace , or both below the heat pump's cut-out temperature?

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #41 – July 25, 2018, 12:43:59 pm

Quote from: Tim – July 25, 2018, 12:36:42 pm

Attached are the dip switch settings, which include:

Heat strip
Heat pump
Furnace / Aquahot

It's not clear if:

1. Can both heat pump and heat strip can be set?
2. Can the logic in the control module handle turning on a heat strip or fuirnace both below the heat pump's cut-out temperature?

Looks like a either/or, type of setting. Who makes the rv ac/heat pump with a heat strip?

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #42 – July 25, 2018, 01:57:31 pm

I have lived with a heat pump since 1979. There are also 20KW of electric strips in the furnace. What they do is if the unit is in heat pump mode and the outside unit freezes up, it will go back to the AC mode to defrost the outside coils and will turn on the heat strips to compensate for the cold air on the inside. When it get colder then what the heat pump can handle it will then turn on the heat strips.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #43 – July 25, 2018, 02:16:33 pm

Quote from: turbojack – July 25, 2018, 01:57:31 pm

I have lived with a heat pump since 1979. There are also 20KW of electric strips in the furnace. What they do is if the unit is in heat pump mode and the outside unit freezes up, it will go back to the AC mode to defrost the outside coils and will turn on the heat strips to compensate for the cold air on the inside. When it get colder then what the heat pump can handle it will then turn on the heat strips.

Had the same setup on my house in Arkansas except return air duct ran under and behind the fireplace so that the air would be preheated before it got to the air handler, if you had a fire going.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #44 – July 25, 2018, 03:53:17 pm

Quote from: turbojack – July 25, 2018, 01:57:31 pm

What they do is if the unit is in heat pump mode and the outside unit freezes up, it will go back to the AC mode to defrost the outside coils and will turn on the heat strips to compensate for the cold air on the inside. When it get colder then what the heat pump can handle it will then turn on the heat strips.

This is the way our home setup works. However, I have found that built-in "trigger" temp for automatically turning on the heat strips is lower than I like. If I wait for the heat strips to come on automatically, the heat pump will be running the outside compressor(s) almost continuously trying to maintain the inside temperature, and they will, like you said, be freezing up repeatedly. I avoid this situation by manually switching to the "heat strip mode". I don't know if there is a way to adjust the temp at which the heat strips are automatically engaged - guess I should research that.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #45 – July 25, 2018, 09:42:46 pm

Our furnace has a few covered plenum exit openings that we uncovered and ran short furnace hoses out into the room which eliminated all high limit shutdowns. Most are not aware that they cycle on high limit. Be glad you are aware and can do something about it.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #46 – July 26, 2018, 08:40:26 pm

Seen the extra holes. Never thought about more runs

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #47 – July 26, 2018, 10:12:16 pm

Yes the plenum has extra holes, and some of those holes are almost completely blocked by the internal heat exchanger tubes. Took a saw and cut the bedroom unit wood enclosure on the inboard side of my coach and eliminated 2 nasty bends in the supply duct. Relocated the starboard aft facing bedroom outlet inboard also (old hole with additional grille is now return air) this also eliminated 2 nasty bends in they supply duct. My Rear furnace is much quieter now, doesn't cycle on high limit, and is more efficient.
Being a HVAC engineer I am kinda anal about this sorta thing. Spent a night in the coach when it was in the low 30's worked great, slept well. Still think I will move the smaller rear furnace to the front of the coach and buy an even smaller unit for the rear for better comfort. Will make Christmas and Thanksgiving trips to the relative's in the KS/MO area more pleasant. WTH even a ski trip to CO.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #48 – July 27, 2018, 08:55:35 am

Foretravel and I needed you way back when. Never found anyone with enough expertise to re engineer that part of the coach you have now.

Re: Advice on replacing both rooftop ACs with heat pumps

Reply #49 – July 31, 2018, 08:31:18 am

One of two ACs are functional, so these are preliminary results. Both Brisk II Air units have been installed along with a new thermostat, the Comfort Control II.

PROS
- Blows ice cold
- No compressor noise from AC
- About 5dB quieter. This is a preliminary result with only one AC running. See attached sound meter screenshot.
- Control kit is somewhat Plug and Play: The 12VDC supply wires had to be validated and the DC ground wire had to be custom-made with crimp terminals. The control kit had to be positioned so that the existing RJ11 control cable could reach.

CONS
- Noise
An annoying 30HZ booming noise is heard in the front and rear of the coach. I am not sure if it is caused by ductwork acoustic/pneumatic resonance or blower vibration. The noise is not heard in the center of the coach.
- Noise
Low-fan setting almost as loud as high-fan. My guess is that Dometic engineering determined that the compressor would freeze up is the fan speed was too low.
- Not DIY friendly
Dometic does not encourage DIY installs because there are no paper manuals. Even the online install guide is lacking full hookup instructions. The outdoor temperature sensor hookup was not mentioned. The thermostat displayed an E4 error "Outdoor temp sensor disconnected" but I figured it out after 1 hour of research.
- Lack of hookup instructions
One multi-zone control kit is required per AC. I only ordered one, so another control box is on order. See part numbers below. The control kit allows programming via DIP switch of your setup: two zones, heat pump, etc...
- Restricted return air flow
Control kit is packaged in a 6x6 inch metal box that is mounted so that it obstructs about 25% of the return air inlet. I am searching for a remedy to this obstruction. The remedy may be re-mounting the box with stand-offs from the inlet filter to provide better air flow. Maybe this is causing the booming sound? The documentation is poor, and allows some flexibility and customizing of the control kit mounting location.
- Bowed template
Torqueing the ceiling template (the metal structure that holds the AC and gasket down to the roof) to 3.5 ft-pounds caused it bow. It should have been designed with more and stronger steel.

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