The new heat pump

The dust is settled.  The tools are put away.  And once again Eolian is warmed by a heat pump.  So which one did we choose, and how did we settle on it?

Our old heat pump was a 16,000 BTU model.  This size was just about perfect for Eolian, as confirmed by the past 5 years of comfort.  This is also about the largest size available to work with 110V (larger units require 220V, which we do not have).

In choosing a replacement, I wanted a unit that provided more protection for itself against failures, in particular a seawater delivery fault.  This could happen as the result of a valving error, a seawater pump failure (happened to us), or a blockage of the discharge (happened to us; it caused the failure of the previous unit).  These are the 16,000 BTU units I considered:

Mermaid

This is the brand of our previous unit.  The new version appears to be essentially the same.   The only protection provided is against freon high pressure.    Allows the use of a conventional thermostat.  Condensor not over the condensate pan.  Starting inrush current works on a 20 amp circuit, as confirmed by our old unit.  ℬ1.700

Webasto FCF

Physical dimensions too large for us.  Huge inrush current of 38 amps - Webasto recommends a 40 amp breaker.  Must use supplied controller.  This unit is not suitable for boats with 30 amp panels.  ℬ1.564

Dometic

Similar to the MarinAire, but without the shroud, gauges.  Also has a different compressor - inrush current requires a 40 amp breaker, like the Webasto.  Not suitable for a boat with a 30 amp panel.  Must use supplied controller.   ℬ1.825

Flagship

Their units come by default with electric resistance heating.  Ummm...  this is no different than using space heaters.  They would build me a reverse cycle unit for, if I remember right, ℬ2.300.  Also, the only protection provided is against freon high pressure.  Allows the use of a conventional thermostat.  Rugged-looking units.

Marinaire

This is the unit we settled on, ℬ1.565.

What I like about it:

• Very well packaged:  sturdy box with polyethylene foam pieces completely filling the voids, multiple strapping, and then the entire thing was shrink wrapped. 
• Supplied from the factory with liquid-filled high and low pressure refrigerant gauges
• Extremely low starting current: 17 amps. 
• The condensate drain pan is stainless.  And it is insulated against sweating.  Three drain locations are provided.
• The condensor coil tube-in-tube heat exchanger is mounted over the condensate pan.  For a heating application this is critical, since the condensor will be quite cold and will sweat.
• The fan can be rotated so that the discharge can be pointed in any direction.
• The fan housing is insulated against sweating
• The fan is very easy to remove - just loosen a hose clamp and disconnect a Molex connector.
• With the fan removed, the unit is only 8" wide - it easily fit thru an existing opening in our under-settee location.
• I see other signs of quality construction.  For example, that fan Molex connector is a locking connector, yet it was also secured with a snap tie, and then secured again with an industrial strength twistie.
• The unit protects itself against damaging operational conditions with the following sensors:
  • Evaporator coil temperature (freeze up, overheating)
  • Freon high pressure
  • Freon low pressure
  • Provision for insufficient water flow protection
  • Abnormal operation protection (not sure what this entails, but the unit is microprocessor controlled, so it could be almost anything...)
• Very flexible mounting options. 
• The unit is entirely covered in a molded shroud.  This protects the delicate plumbing from damage and provides additional sound insulation.
• The unit is very quiet - really, all you can hear is the rush of air into the cabin.
• Fan speed is automatically controlled, rising and falling as conditions dictate.
• Condensor tubing is internally grooved, improving freon heat transfer
• Evaporator is coated with a hydrophilic coating so that moisture condensing on it (in air conditioning mode) does not bead up but instead runs off in sheets, improving heat transfer from the air.
• COP of 4.5.  That is, for every kilowatt-hour drawn from the ship's supply, 4.5 kilowatt-hours of heat are delivered.  More simply, the heating efficiency is 450%.

What I don't like

• No provision for a conventional thermostat - you must use the supplied unit.
• The supplied unit is not a thermostat; it is a controller.  It is powered from the main unit, with no battery backup.  While its eePROM retains previous settings, the display is off when there is no shore power.  In particular this means that when we are at anchor we have no reading of cabin temperature.
• The supplied unit only has a single temperature setpoint - there is no provision for having the setpoint automatically drop at night and rise in the morning.  In particular, with this unit I must get up in the cold to turn up the heat.
• Temperature is not measured at the controller as you might expect.  Instead it is measured at the return air entrance, and reported at the controller.  If the air in the boat is well-mixed, this makes little difference.  If not, the controller needs to be set to a lower temperature to prevent over-heating the boat.
• The lowest temperature setting that can be set in heat mode is 61°.  With our previous unit, when we were away from the boat I set the temperature to 55°.

Meh items

• The unit has a humidity management mode.  If we were in a humid climate, this might be important.  But not here in Seattle.
• The unit comes with a remote control. 

[We also considered diesel-fired heaters, like the Webasto.  These would have had the advantage of supplying us with the same heat at anchor that we have at the dock.  But with diesel at $4-5/gallon, a diesel-fired heater cannot compare cost-wise with a heat pump that delivers roughly 5 kwh heat for every 1 kwh purchased.  The break-even cost would be about $0.76/gallon diesel.  Also, there was the problem of where to run the stack.  Finally, neither of us like the jet-engine noise of the diesel heaters.]

The new heat pump