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[KevinE]

I am looking for a system to control the heat settings while my boat is stored in the winter. Basically, the boat needs to be kept at a temperature above the dew point in order to prevent condensation inside and hence, mould growth (the problem). For my approach, I will need 2 temperature sensors (one inside, one outside) and a device to measure the relative humidity inside the boat.  Given the temperature and relative humidity, I can calculate the dew point. I can compare with dew point with the outside temperature and thus ensure the temperature inside the boat is maintained a few degrees above the dew point.

So being new to x10, I am looking for some ideas on the best way to implement this. I will need to program the logic to run this system on a computer and then ideally download that to a PLC which I would put on the boat. As always, I am looking for the most economical way to do this as there is limited energy savings to offset the cost of the equipment. What are the best temp and humidity sensors to use? The boat has 110v elect. system and I use 2 heaters inside so ideally I would like to control the 2 heaters through the 110v lines. I also have a dehumidifier on board which I may want to control also (low humidity lowers the dew point, which in turn allows me to store the boat at a lower temperature).

Any help would be much appreciated - the number of ways to do this is quite overwhelming and I have no x10 experience!

Kevin

[steven r]

Wow! That's challenge. Hope someone can help. How are you thinking about doing a "realtime" dew point calculation? Could you use a working compromise that keep the inside temperature higher than the outside? Even with an AHP macro you would need to get the logic down to true / false conditions. You couldn't calculate a due point in AHP and then have it test for this variable temperature value.

To clarify something for us, what is source of 110V for the boat? i.e. Is the boat being stored on land plugged into a 110V power source or is it's 110V source from a battery inverter system? (AC from a battery inverter doesn't work well for X10. Modules tend to fry.)

[Charles Sullivan]

Designing a simple system to do this is not all that difficult.  Designing a system which is fault-tolerant enough to protect you from major financial loss when the inevitable failures occur is another matter entirely.  (What would it cost for mold removal if the system failed?)  The use of the X10 protocol for transmitting control signals over the existing 110V electrical system would be a weak link in any system you could devise.

[Oldtimer]

Designing a simple system to do this is not all that difficult.  Designing a system which is fault-tolerant enough to protect you from major financial loss when the inevitable failures occur is another matter entirely.  (What would it cost for mold removal if the system failed?)  The use of the X10 protocol for transmitting control signals over the existing 110V electrical system would be a weak link in any system you could devise.

Amen to Charles Sulivan's comment because the system might have to operate without any human observation for days or weeks at a time. For the record I have found that X10, with appliance modules modified to defeat local control, works quite well in home situations where there are people around to be aware of what's going on.

Let me offer another solution based on personal experience.  I have lived on the shoreline, in a house with estuary water on three sides, for 15 years.  When I moved here I set up the small building on the back of our garage as my workshop by putting vapor seals, insulation and plywood on the inside walls.  My concern was protecting several thousand dollars of tools and our two bicycles from the corrosive, sometimes very humid atmosphere (you quickly learn to use stainless steel fasteners for everything in this environment) There is no continuous heat in the shop but I installed a 75 watt boat closet heater that runs 24/7 unless the temperature gets above 75 degrees.  The shop is about 120 square feet and this arrangement maintains a 5 to 10 degree differential all year round (most of the exposure to condensation is in the Spring and Fall not Winter or Summer).  As a result I have never had a rust or corrosion problem with anything in the shop.  I quickly learned however that I have to keep all the drawers and cabinet doors open a crack to maintain air circulation inside them.  By the way, even though the walls are vapor sealed there is enough leakage arround the door to provide a small amount of air exchange with the outside.

The major difference I see between your boat and my shop is that I don't have a bilge underneath the floor which could keep the humidity higher from evaporation.

I too spent a lot of time thinking about differential thermostats and humidity detectors but finally gambled on the simple system described above and am very pleased that it has worked out so well.

[steven r]

Designing a simple system to do this is not all that difficult.  Designing a system which is fault-tolerant enough to protect you from major financial loss when the inevitable failures occur is another matter entirely.  (What would it cost for mold removal if the system failed?)  The use of the X10 protocol for transmitting control signals over the existing 110V electrical system would be a weak link in any system you could devise.

While I'd love to see the "simple system" that can calculate the dew point, I have to agree 100% that X10 would be the weakest link in the system. You couldn't of expressed it more clearly.
I learned a long time ago to use redundant timers for things that really needed to be off. i.e. My shutdown macro turns things off twice like the coffee pot. (I don't make a lot of coffee but when my mom visits she's been know to leave it on all day.)

[KevinE]

Thanks for all the replies - I was hoping somebody would just say now here is what you need.....

Old timer, what you do right now is what I do - I leave a heater running right now that keeps the boat between 50 and 60 degrees irregardless of what the temperature is outside. My reasoning for the system is 2 fold. Firstly, on the colder months of the year, it costs me about $80 a month to heat my boat (38 ft long, uninsulated). As a result of this, I want to keep the boat as cold as possible without going below the dew point which changes constantly. I can lower the dew point by reducing the humidity with a dehumidifier.

I took a look at the Ocelot home automation controller which also has temperature and humidity sensors. The programming language is rather crude, in fact I wouldn't be able to calculate a dew point as there a floating point calcs involved and natural logs etc.
So really it seems I need a PLC with a somewhat robust programming language. Any thougths here?

-Kevin- 

[Charles Sullivan]

I took a look at the Ocelot home automation controller which also has temperature and humidity sensors. The programming language is rather crude, in fact I wouldn't be able to calculate a dew point as there a floating point calcs involved and natural logs etc.
So really it seems I need a PLC with a somewhat robust programming language. Any thougths here?

Do you really need all that?   For a given relative humidity there's a minimum temperature required to stay above the dewpoint.  It would seem that an integer table lookup with 100 humidity percentage points as the independent variable and one degree temperature increment as the dependent variable ought to be sufficient, or even 50 points at 2 percent humidity increments.  (Of course you'd have to check this in a loop since the relative humidity will change with temperature.)   The table would be precalculated, including whatever safety margin in temperature you felt comfortable with and whatever corrections might be necessary for nonlinearity in the sensors.

[steven r]

...I can lower the dew point by reducing the humidity with a dehumidifier...

Does your dehumidifier allow you to set a level of humidity or does it just run continuously? If it is setable, that would make determining the dew point a lot easier.

[Oldtimer]

Old timer, what you do right now is what I do - I leave a heater running right now that keeps the boat between 50 and 60 degrees irregardless of what the temperature is outside.

Kevin E I need to clarify what I posted.  The 75 degree limit is where I turn off the heater not what I keep the temperature at, the rest of the time the heater runs continuously.  Because the heater is so small it is only able to maintain the temperature in the shop between 5 and 10 degrees above whatever the outside temperature is.  As a practical matter you only need it between freezing and 75 degrees to keep the dew point from causing a problem ( I haven't bothered to install a low temerature cut off but with energy prices up I'm thinking of it).

To give you an idea of how well the 5 to 10 degree differential over outside works I had a leak in the roof last year (caused by some tree surgeons walking on the old asphalt shingles) that let significant water onto the shop floor (not anything else thank goodness).  In spite of the extra water I still didn't have any rusting on any tools!

I don't know how big your current space heater is but it's probably much more than you need for what I'm talking about.  You'll need to experiment, probably with several small closet heaters and a simple inside/outside thermometer to see how little continuous wattage you can get away with.  Once you're done you'll save a lot on your electric bill and won't need to buy any fancy control equipment.

By the way we use three smaller heaters in closets in our house in the summer to eliminate mildew and they work perfectly.

P.S.  I don't know how many or what kind of heaters you have now but if you have more than one there are two ways to reduce their current drain.  One is to install a power diode in them.  The other is to hook them in series.  Or, do both.  This could save you having to buy more stuff while cutting your electric bill significantly.

[TakeTheActive]

P.S.  I don't know how many or what kind of heaters you have now but if you have more than one there are two ways to reduce their current drain.  One is to install a power diode in them.  The other is to hook them in series.  Or, do both.  This could save you having to buy more stuff while cutting your electric bill significantly.

"Years ago...(Yeah I know, 'In a galaxy FAR, FAR away...') ", I added SECONDARY inline switches with 1N4001 diodes into all of our incandescent HANGING LAMPS to achieve ~50% dimming.

Is this what you're referring to?

[Hooking them in SERIES I can understand...  Same difference...  ]

[Oldtimer]

P.S.  I don't know how many or what kind of heaters you have now but if you have more than one there are two ways to reduce their current drain.  One is to install a power diode in them.  The other is to hook them in series.  Or, do both.  This could save you having to buy more stuff while cutting your electric bill significantly.

"Years ago...(Yeah I know, 'In a galaxy FAR, FAR away...') ", I added SECONDARY inline switches with 1N4001 diodes into all of our incandescent HANGING LAMPS to achieve ~50% dimming.

Is this what you're referring to?

[Hooking them in SERIES I can understand...  Same difference...  ]

Exactly.

[gil shultz]

Just a thought,

Light bulbs (tungsten) generate mostly heat not light but when used as small heaters they make it easier to read the thermometer.  redundant lamps are cheep.

Gil Shultz