Reverse Cycle Heat (Velair) Delta T is colder water?

[Mark424]

I'm looking at a boat that has 2x 16K BTU from Velair that has AC and reverse cycle heat. I've not been able detailed answers from the Velair folks. They say the reverse cycle heat will operate as long as sea water is above 41 deg F, but they aren't saying what the Delta-T will be, e.g. when the sea water is 45, 50, or 55, what is the temp of the warm air the system can put out.

Anyone have any real world experience running these units for heat in cooler (45-55 F) water? How warm is the air they put out? What size boat? outside temp?

One other question, curious if running a Velair in reverse cycle heat will dehumidify. e.g. if I supplement the heat with a portable propane heater for more BTUs, will the Velair pull the moisture out that the propane heater is generating?

Thanks!!

[hlev00]

I can't help you on the first as I don't have this model. I have another vendor's unit but same basic technology.

First, if you are suggesting heating with unvented propane that is dangerous due to risks of carbon monoxide build poisoning.

However in such a situation, the reverse cycle heat won't dehumidify. De-humidification only happens in cooling mode because as the temperature of the air is cooled, some of the moisture condenses out of it, resulting in 1) drier air and 2) condensate that has to be removed from the boat. In theory you could run it in cooling mode with the propane heater and that would remove some humidity. This is what happens in a car to defog. But, you will be going backwards on your attempts to heat the boat. In a car there is no additional moisture being added from the heat exchanger.

Look at a vented propane or solid fuel heating source to add more heating capacity. Even then, humidity and condensation build up can be a real problem in cold climates if the boat is not insulated well.

Harru

[Coolerking]

Are they self contained units?
If the are split type systems, it may be possible to install a heat strip that can be used when the water temperature prevents the reverse cycle from heating efficiency.
There are also inline duct heaters that are available.

[wefleenor]

I put in 4 Velair units just 3 months ago. Here in Portland OR the water temperatures do get that low and I had to run the units on a low fan setting. At that I get an occassional error on one unit, twice so far. I have 3 units at 16K and one at 21K. Living area is entirely above the waterline in my 49ft long, 23ft wide power catamaran. Even the heads/showers in the hull are above the waterline. Pilothouse is all windows on 3 sides. Even on the low fan setting the units have no difficulty heating the boat.

[rslifkin]

My units aren't Velair, but I do have a 16k that's currently running reverse cycle heat, and my boat is currently sitting in 46 degree water. I'll be there this evening, so I'll check a few temperatures for you. The unit was putting out good heat yesterday, and with 50 degree air temperatures it had no trouble getting the cabin up to 70* from cold and keeping it there, and the air coming out of the vent was definitely warm, but not hot.

When running in reverse cycle, the unit won't remove any moisture from the air. It only adds heat. So it'll reduce relative humidity by making the air warmer, but it won't reduce the actual amount of water in the air. However, if you've got the cabin 20+ degrees above outside temperature, a small amount of air exchange to the outside will usually be enough to keep humidity from being a problem.