Wet heating systems

[John100156]

sorry john just read your post which I don't really get if I am honest but after all that

which system do you say is best

OK sorry - here goes:

First you must decide if you want to ventilate the space or simply heat it, if you simply want to heat it a water system would be OK, but it will heat slowly. Whenever air is heated (with a wet system over the rad) it will expands in volume but no moisture is added (assuming no occupants at this stage) so it will always dry-out anyway, exactly the same whether internal air is heated with a radiator or circulated and heated by a fan (of course when taking in fresh air this will change the mix moisture level).

You are likely to have a healthier indoor air quality (IAQ) when you use and air system, that brings in some fresh outdoor air. You will likely keep all air paths tightly shut in winter. You also need to be cautious if you are cooking in a space with gas, it may need additional air to ensure proper combustion and dilution of Carbon Monoxide, you do not get this with a wet rad system.

Advantages of a wet system might be:
1) You can place heat emitters (rads) where you want them.
2) You can pipe it around the boat easier, smaller pipes to route.
3) People can find their space -hotter near rad.
4) Easier and cheaper to install.
5) Less noisy - you can hide circulating pump away somewhere.

Disadvantages might be:
1) Does not cater for any significant ventilation load.
2) Greater fluctuations of temp around the space.
3) Slower to heat the space or raise fabric temps.
4) Does not dilute any dangerous gasses building up in a boat.

Advantages of Air heating system (heat pump or fan heater) might be:
1) Will heat air quickly due to its low thermal heat capacity - good for intermittent occupation.
2) You can mix with fresh air and filter to provide a much better indoor air quality.
3) No water in system or bilges if it leaks - although you are likely to go for a sea-water not air source heat pump which has water.
4) Significant reduction in recurrent energy using a heat pump - minimum 3kW heat for 1kW electricity.
5) You get the benefit of cooling also with a heat pump.
6) Can provide air for combustion if using gas.

Disadvantages might be:
1) Difficult to route ducts and install equipment in a boat.
2) Can be noisy if system is not properly sized/installed.
3) Fans and Heat Pump packaged units can be difficult to fit.
4) A lot more expensive to install even when taking into consideration energy benefits, if infrequently used pay-back would be long.
5) Need to be properly sized and designed - i've seen a lot of bad systems and have been working in this field since 1973.

So, its horses for courses, you need to make an informed choice.

I would probably go for heat pumps (but my boat is in the Med), don't get me wrong, if I was designing a perfect system I would pipe/circulate chilled water and low temperature hot water to indoor fan coil units and I would ventilate and mix the fresh with room air to ventilate the boat and get precisely the right humidity, using the system to de-humidify when required.

On my boat I simply have two heat pumps.

Hope the above helps.

 

[John100156]

.....Also, a hot air system dries air really efficiently. Why is this an issue? Dry air causes dry eyes and dry and sore throats. Hence, another tick in the box for choosing a hot water system.

Another tick, oh dear: If I heat air in a room from say 10C to 23C with a rad, its moisture content is exactly the same as when I heat it with a fan heater - you have not added any moisture to the air/process so its relative humidity would be the same......:ambivalence:

 

[John100156]

Finally, someone mentioned a heater matrix or wet heater battery in an indoor air handling unit - that is a good compromise if you do not wish to go for a refrigeration process/heat pump.

Less efficient than a heat pump, but you can easily pipe hot water to the indoor air handling unit matrix/coil and add a small fresh-air duct to provide better IAQ. If your clever you can configure a change-over in summer and use the heating pipes as cooling pipes, running chilled water through them (need to consider good pipe insulation and a condensate tray on the indoor coil). Would be reliable, easier/cheaper to maintain and route pipes/smaller ducts than a heat pump but less efficient. Also need to insulate fresh-air duct to avoid condensation when bringing in fresh-air in winter - but you could put dampers on it so you use recirculated air only when the boat is unoccupied and heated up or even CO2 detectors only to let in fresh air when the levels increase.

Enough from me for now......

 

[Piers]

My Sunline had a fan assisted heater matrix, and we never used it, due to the noise of the fan, it was really intrusive. You also have to be careful that the water does not freeze up when you are away from the boat. Popped the matrix our first winter.

The fan matrices in Play d'eau are fairly quiet. The fans are no driven by a pulsed 24vDC so when less heat is needed it isn't the voltage that's dropped which makes the motor really noisy, not the 24v is pulsed less slowly, so there's really little noise.

 

[John100156]

Yes - you can go for variable air volume when using a hot water heater battery generally referred to as a fan coil unit to control heat output, you can also us a three port valve to vary the flow of hot water through the coil to give you closer control over the supply air temperature (ts) and space temperature (tei).

A well attenuated and insulated small diameter fresh-air duct could also be routed, to mix with room air at the FCU with damper to open fresh-air only if CO2 levels rise. Just need to make sure that you room temp sense (some FCU's use a return air sensor which will of course be skewed by the temp of the fresh-air mix).

 

[John100156]

Now for something quite radical:

Many of us have hot water calorifiers on our boat that heat our hot water. We often have an option to heat them from waste heat from our engines. What you could do is fit an over=sized one,that has the two engine option, using the second to pump low temp hot water around the boat, ensure expansion vessel and PRV is installed, perhaps even two calorifiers - all very simple to engineer really.

Anyway this really is my last post on this subject...

 

[skinnylegs]

David

We have an American boat that has 5/6 units for reverse cycle heating and air con, the air con and heating only blow room temp air so I dont believe it is working, although all the controls, fans etc work in the rooms. Would be interested to understand how to incorporate a boiler into the system. Is it a case of taking the existing pipe work and pumping hot water around the pipes to the fan matrix in each room i.e flow and return.

Thanks