Inland waterways min temperature

[floater]

Strange question, Any idea what the minimum water temperature would be approx 12"-18" deep? I'm guessing 1 to 5.c

 

I'm looking into the possibly of building a water source heat pump for me new boat

 

If not I'll measure it in a few months time

[stort_mark]

Strange question, Any idea what the minimum water temperature would be approx 12"-18" deep? I'm guessing 1 to 5.c

 

I'm looking into the possibly of building a water source heat pump for me new boat

 

If not I'll measure it in a few months time

 

No idea but water source heat pumps are being introduced in China in big numbers and they seem to be taking water from about that depth.

[Justme]

So like a reverse skin tank then.

 

or pipes wrapped round the hull or a double skined base plate.

 

Justme

[floater]

So like a reverse skin tank then.

 

or pipes wrapped round the hull or a double skined base plate.

 

Justme

 

The surrounding water would receive heat when in cooling and provide heat when in heating via some kind of heat exchanger possibly either skin tank or raw water (depending on min temp). Also needed are compressor(s) expansion valves and indoor heat exchanger and a 4 way valve plus other refrigeration equipment and controls.

 

It would probably make a very efficient system with a COP (coefficient of performance) of 3-4 i.e put in 1 kw get out 3-4kw. (depending on temperature difference.)

 

Most ground source and water source heat pumps require a deep stable source.

 

I could use air source but it might be a little noisey for the neighbours

 

Minimum water temperature is required to find out the minimum evaporating temperature/pressure during heating

 

Just in case your interested

[Tony Brooks]

The surrounding water would receive heat when in cooling and provide heat when in heating via some kind of heat exchanger possibly either skin tank or raw water (depending on min temp). Also needed are compressor(s) expansion valves and indoor heat exchanger and a 4 way valve plus other refrigeration equipment and controls.

 

It would probably make a very efficient system with a COP (coefficient of performance) of 3-4 i.e put in 1 kw get out 3-4kw. (depending on temperature difference.)

 

Most ground source and water source heat pumps require a deep stable source.

 

I could use air source but it might be a little noisey for the neighbours

 

Minimum water temperature is required to find out the minimum evaporating temperature/pressure during heating

 

Just in case your interested

 

 

Unless you intend to run a generator (so why not use its cooling system) or use a shoreline looking at you figures I am a bit concerned about how you intend to supply the electrical load. Thinking about how a 1.5 kW stove heats a boat I reckon you may need 300 to 400 watts of power and that is a large amount to supply 24/7 from batteries and "normal" charging.

 

However its very interesting so keep it up and give us regular reports.

[PaulG]

Strange question, Any idea what the minimum water temperature would be approx 12"-18" deep? I'm guessing 1 to 5.c

 

I'm looking into the possibly of building a water source heat pump for me new boat

 

If not I'll measure it in a few months time

 

Generally speaking, as the temperature of water falls, it becomes more dense, and will therefore sink. Alternatively, as water warms, it becomes less dense, and will therefore rise.

 

However, at about 4 degress C, this process is reversed, and water starts to expand as it cools until it freezes into ice, which is very obviously is less dense than water, as it floats.

 

So you would expect to find the coldest water at the surface. Certainly in deep lakes, the water temperature does not fall below 4 degrees C because, below this temperature, the water must cool by conduction, which is a much slower process than cooling by convection.

 

Of course, this is only true for still water. Running or turbulent water would be at a consistent temperature regardless of depth.

 

Hope this makes sense.

[US Marines]

Certainly in deep lakes, the water temperature does not fall below 4 degrees C because, below this temperature, the water must cool by conduction, which is a much slower process than cooling by convection.

 

Sorry, confused here - the temperature of water at the bottom of deep lakes is usually around 4 degrees Celsius because, as you have said, water is densest at this temp, so it sinks to the bottom when there is no strong current. The temperature higher up in the water profile can be - and often is - colder than this, and I'm not sure how conduction and convection come into it ?

[US Marines]

Strange question, Any idea what the minimum water temperature would be approx 12"-18" deep? I'm guessing 1 to 5.c

 

I'm looking into the possibly of building a water source heat pump for me new boat

 

If not I'll measure it in a few months time

 

Just saw this on the Scottish Building Standards website:

 

canal heat pump

 

It doesn't answer your question I don't think, but it might be interesting and they might be able to give you more information and/or tell you their experiences of winter operations....

[floater]

Unless you intend to run a generator (so why not use its cooling system) or use a shoreline looking at you figures I am a bit concerned about how you intend to supply the electrical load

 

I'm residential and will be on shore hook up. I normally use a 2 kw electric convection heater except when <0.c outside then i switch to the kabola.

 

For my larger new boat, a 60 x 12'6" barge, i'd plan on about 6 kw heating/cooling. Possibly using 2 compressors in stages to allow control and reduce high torque loads from compressor start up.

 

I'd also be able to run the system when cruising from my 24v 100 amp alternator (Probably by limiting a compressor). Possibly through inverter if the compressors end up being 230v. (i appreciate this will be less efficient and therefore subject to losses)

 

I'd also have a solid fuel and possibly small 2nd hand 5kw eberspacher on board for when not on shore power or if the unit fails due to poor design

 

Thanks for the info. I'll chase it up and see if any data is available.

 

I'm only toying with the idea at the moment and it'll be a while before i design it, if i do. Although i dont fancy paying the crazy fuel and £3K+ unit costs for marine diesel heaters especially due to the relative poor efficiency.

Edited October 1, 2008 by floater

[PaulG]

Sorry, confused here - the temperature of water at the bottom of deep lakes is usually around 4 degrees Celsius because, as you have said, water is densest at this temp, so it sinks to the bottom when there is no strong current. The temperature higher up in the water profile can be - and often is - colder than this, and I'm not sure how conduction and convection come into it ?

 

Above four degrees C, cooling the water at the surface sets up convection currents as the cold water sinks and warmer water rises to the surface.

 

Once the water temperature has cooled to four degrees, the less dense cold water stays at the surface, so convection currents cease. Any further cooling in the lower layers is by conduction. Water is a poor conductor of heat, so cooling by conduction is a much slower process.

[US Marines]

Above four degrees C, cooling the water at the surface sets up convection currents as the cold water sinks and warmer water rises to the surface.

 

Once the water temperature has cooled to four degrees, the less dense cold water stays at the surface, so convection currents cease. Any further cooling in the lower layers is by conduction. Water is a poor conductor of heat, so cooling by conduction is a much slower process.

Thanks - but I thought water was a relatively good conductor of heat (23x better than air) ?

 

My understanding is that it is that water in deep lakes stratifies when it reaches 4 deg C simply because the densest and coldest water sinks to the bottom - and that progressive layers upwards get colder. It remains like this is simply because the stable conditions lead to no mixing taking place (which I guess could be a lack of 'convection'). My undertanding is that the reason that it doesn't get colder at the bottom isn't because water isn't a good conductor of heat but more a function of the depth of the water column above it coupled with Newton's Law which says that the rate of cooling is proportional to the difference in temperature between one layer and the next....

 

No matter - we're both talking about the same thing anyway !

[richardf]

We run a ground source heat pump here. We are based in an old water mill and the supplier was at pains to make sure that there was a flow of water out of the mill pond where the heat exchanger pipes are located - or otherwise we could end up freezing the lake. Now that would be a bit of a shock for passing boaters couldn't it!

[floater]

We run a ground source heat pump here. We are based in an old water mill and the supplier was at pains to make sure that there was a flow of water out of the mill pond where the heat exchanger pipes are located - or otherwise we could end up freezing the lake. Now that would be a bit of a shock for passing boaters couldn't it!

 

Sound's like a weapon dick dastardly might have fitted to his boat.

 

As we'll be most likely pumping the water in , through the heat exchanger and out again then the minimum outlet temperature of the water would have to be above freezing, so it won't be a problem.

 

It could be a problem if i used an undersized skin tank, however i think i'd have problem's on the boat first. also as the cooling capacity will be around 6 kw it wouldn't be possible to freeze a large volume. (like having a small heater in a big room)

 

I'd be interested to know more about your setup. (Kw capacity, design parameters, installer, equipment used, manufacturer of equipment)