Visit our Popular Forums

**James S** · 10-02-2010, 09:06

I'm throwing this out for some out-of-the-box thinking.

Ideas on how to store HEAT on a boat..could be fluid...solid...gasious?
I've been looking at the evacuated tube solar collectors lately and its just got me thinking...if we can easily capture heat just below the boiling point...what are some efficient ways (weight, volume, longevity) of storing it?

some info on the collector tubes
http://www.savoiapower.com/heatvac.html

Bash · 10-02-2010, 10:11

engine block heater? It seems that the engine is a natural heat sink.

um saudade · 10-02-2010, 10:47

Do you wish to store heat or energy? A big difference.
In spite of the inefficiencies of the system, I think that the use of storage batteries is probably the most efficient method of energy storage on a boat. You must consider what is available and what is the final use of the energy you have stored.
If you wish to convert the energy (now stored as heat) into electricity you must convert the form and all conversions are energy hungry.
Furthermore, long term storage of heat requires a lot of mass and where to put the mass on a boat where space is critical. Second, the mass must be well insulated and the insulation takes up a lot of space.
Third, if the heat stored is to be used as something other than simple heat (as in space heating) the heat must be converted and not even considering the inefficiencies of the conversion, the equipment takes up space.
I’d work on building a better storage battery.
Um Saudade

**James S** · 10-02-2010, 10:59

The idea is to store heat.
The keel is an area that has potential since weight is advantagise..and insulating volume may be incorporated.
So what if you stored just heat and with some enhancement from other fuel used it to power a Stirling engine...or to enhance convection, as part of another system....or used it to preheat other applications that we would otherwise use other energy sources to heat?

LakeSuperior · 10-02-2010, 11:01

There is seriously alot of heat already stored in the seawater around you (how's that for "out-of-the-box-thinking"?) A heat pump would be a most efficient way to extract some of the heat. They make heat pumps for marine applications. I have two in my Bertram.

There are a couple thermodynamic laws that you will be forced to obey when you try to store and extract heat. You don't need to know what they are however you will be working within those rules when you venture into this domain.

anjou · 10-02-2010, 11:06

What is the intended environment James?
Thermal mass is the traditional way to store but its not conducive to the limitations of a boat.
Solar thermal could be used to power a sterling engine which in turn provided heat and power.

Captain Bill · 10-02-2010, 11:07

One of the best ways to store heat is in a sealed container of anhydrous salts. There are a number of salts that release heat when hydrated from an anhydrous state. They can be dehydrated again by the application of heat. To get heat back out simply add water. This would seem to be an ideal way to store "heat" because most of the heat is not stored as a temperature differential and cannot be lost to the surrounding environment as long as the salt remains sealed. There is even a scheme to use this process to provide refrigeration. If one has a separate container containing an ethylene glycol and water mixture and connects the two containers together the anhydrous salt will remove all water from the tube causing evaporation of more water from the mixture. This evaporation requires heat so the glycol mixture gets cold. My understanding is for best results one should pull a vacuum on the system to lower the boiling point of the water. I saw a scheme where the plan was to use flat plate collectors to do this in sweden but evacuated tube collectors have higher temperatures and would be more efficient. The biggest issues are that the salts weigh a lot and require a sealable container. I think the guy in sweden was claiming he could store about 80% of the energy collected.

**James S** · 10-02-2010, 11:09

Yeh that not in the box.

I'm thinking 80-90c......hot heat.

RDW · 10-02-2010, 11:13

To store heat you would have to have a mass that you would transfer the heat to. On a sail boat you would not want to add mass just to store heat so you would use what you had at hand. The only things that come to my mind would be water and fuel as heat sinks. Take this with a grain of salt. I am totally green.
rdw

Captain Bill · 10-02-2010, 11:14

Once "charged" the rate of heat recovery and thus temperature were controlled by the rate at which the salts were rehydrated. The faster you added the water the higher the temperature. What are you looking to use a 80-90c temp. for?

**James S** · 10-02-2010, 11:19

Hey Anjou....the Stirling was my initial thought but I see some other "support" type usage as well.

Bill..now thats interesting about the salt!
The refer thing you mentioned is also on my mind...I think its called the "ice ball" or something like that....
I'll be doing some searching on the salt thing?

Captain Bill · 10-02-2010, 11:29

Unless you plan to use the heat in very short order there is no way to store heat in anything that requires a temperature differential. All systems depending on thermal mass depend on a temperature differential and loose heat to the surrounding environment. It's basic thermodynamics. Heat flows from hot to cold and while you may slow it down you can't stop it. The anydrous salts will cool off to match the temperature of the surrounding environment thus loosing a protion of the energy stored in the container, but once the temperature equilabrates no more loss occurs. It's very much like a storage battery for heat. I expect that there are significant engineering issues to overcome such as these salts tend to be highly corrosive to metals, yet metals make the best heat exchangers. I don't think this is something available off the shelf.

**James S** · 10-02-2010, 11:44

Bill
So if the salt like stuff was stored in a suitable container, that was highly insulated...perhaps with those thin vacuum panels used in refrigeration.....and there was a matrix of heat exchanger coils of chrome plated copper or some other as yet to be determined material (that does not react badly with the salt like stuff)...that would both heat the/dry the salt...and remove the heat from it as it is hydrated....am I understanding this so far?

Captain Bill · 10-02-2010, 12:03

It's been some time since I read the article on this guys system in sweden and I'll try to recall exactly where I read it. As I remember he set up the containers to hold one metric ton of salt. Keep in mind he was heating his house in sweden with this so the numbers are going to sound big. Each container was insulated. This was to keep the heat in so that it could recharge the salt or be extracted to heat the house rather than be lost to the enviroment because the temperature is raised when charging or discharging the salt. Each container had two heat exchange coils, one for charging and one for using plus a connection to a water source. His claim was that he was able to get through a swedish winter with 9 metric tons of storage. I don't specifically remember what salt he was using but I do recall him saying it was a byproduct of sulfur scrubbing from power plants so I imagine it was some kind of sulfate.