Heat accumulator

[Phantom]

I believe that commercial/industrial grade paraffin has a higher flash point so that will help with the flammability issue. If the wax is away from a flame there should not be any issue with it igniting.

Before I go any further does any one have do's and do not of putting a wax fire out?

[Clev]

Don't put water on it. Ask me how I know.

[osolemio]

Originally Posted by Indyplumber

I have a question about storing the extra heat generated during the day. What is the best commonly available medium to use? I have a basement and crawl space to put something in but nothing large. Would a 4ftx4ftx4ft concrete block, very well insulated and buried in the ground, with PEX tubing running through it work? Can't really have a
1-2k gallon tank anywhere. I understand the efficiencies probably wont be good but I want to make a system as cheaply as possible using common materials.

The best place to start is the heating system itself. The optimum is a large mass, like a thick stone or concrete floor with built in liquid (hydrating) tubing for heating. It takes ages to heat it up, but also ages to cool down. So you can heat it when you have the sun, and let it cool down at night. The more the mass, the better!

A small area, high temp radiator based system, as well as air based systems, are less efficient if you have a variable heat supply like you have from solar power. Turn your aircon/HVAC off, and your house will heat/cool quite quickly.

A second advantage is that underfloor heating (large mass and area) requires a lower temperature. This is not as important when burning fossils, but essential in solar heat and heatpump installations. The more your heating system can cool the solar heat panels, the more energy you can extract.

Also, if you store heat other places than the floor (for instance in the clay/earth/sand under your house), a large mass - low temperature heat storage loses less energy than a small mass - high temperature storage.

In the project I am devising, I am using several ways of storing heat. Long term storage is under the house (which is clay down to about 7 feet). It is being insulated on the sides, which means most of the energy loss is actually up through the floor and into the house - which is no loss at all. Storing heat during daytime, I have a total capacity of just over 1000 USG (including the main heat buffer).

During summer, when production is high and demand is low, I can absorb as much heat during day as possible, into the clay, as well as the 1000 USG water capacity. During nighttime, the water tanks can keep transferring heat into the clay in anticipation of the next day - to prepare them to be able to absorb more heat. I intend to sync weather prediction data into the system, so if the following day is overcast/cold/windy, I will keep the heat in the water tanks for use during that day and possible the next ones.

I am sorry that I cannot give many more details - or proof - yet, as the system has not yet been finished. When it is up and running, I will supply both proof as well as more detailed information of how it is working. Including some graphical presentations which hopefully will be easier to understand than my mumbling above!

Water and PCM are amongst the better heat storage mediums normally. But for large storage capacities, they become expensive and it is not so easy to build a house on top of a 25000 USG tank of water. Although clay, stone and sand generally only hold about half the heat of water, they are usually there, under your house, already. All you need to do is shoot pipes into it, in a way where you can store and possibly extract heat.

As for PCM specifically, the high grade professional stable material is so expensive that it is only worth while if it changes phase on a daily or at least weekly basis. 3/4 of my 1000+ USG water storage capacity is prepared for insertion of PCM modules, should I later choose to do so. They would most likely be set around 120-140F or so - this means I can store more heat on a good solar day compare to a plain water tank. But I need to see first how many days a year the water tanks reach max capacity. I might even consider a mix, maybe a set of ~ 100F and some at ~ 140F to get different "steps" of capacity increase for different situations.

See also "annual geo solar heating" and similar, for more information on this matter.

[AC_Hacker]

Originally Posted by osolemio

See also "annual geo solar heating"
and similar, for more information on this matter.

Outstanding post, many underlying principles explained.

Lots more info at your suggested link (above).

-AC_Hacker

[osolemio]

Originally Posted by AC_Hacker

Outstanding post, many underlying principles explained.

Lots more info at your suggested link (above).

-AC_Hacker

Thanks!

This is what made the foundation of the seasonal storage function of my system:

Greener Shelter

The system mentioned above is driven by convecting air, driven merely by the flow created as the density of hotter and colder air starts circulating.

My system is waterborne (hydronic). But note that I do not circulate the same liquid all over the system. Basically, there are three main "blood vessels" in my system:

Heating system, connected to a 100-house central heating gas fired (mandatory subscription) system. This circulates in the 2750 USG main water buffer, as well as into underfloor heating and radiators. It is pressurized as these systems normally are.

External storage system: Also water based, but a separate system. The water pressure is much lower here, just the normal pressure of about a 10 feet water height. This goes into the three 300 USG water tanks, into the underhouse long term seasonal storage, and around the foundation for another reason I think I explained before.

The last one transports the heat between the two circuits mentioned above, and the solar heating panels. I can direct and redirect as I wish, to transfer between either of the two, or all three of them, using several valves. This one is glycol based, as it will freeze at times during the winter.

All three circuits are connected using two heat exchangers. One built into the main water buffer connects the two water based strings, and the external storage string is connected via an external separate heat exchanger.

Check my previous posts, I have posted diagrams earlier - simplified ones.

[osolemio]

Here you can see a schematic (system is modified somewhat, but it shows the principle) http://ecorenovator.org/forum/renova...old-house.html

Other relevant posts:

http://ecorenovator.org/forum/solar-...ing-house.html

http://ecorenovator.org/forum/conser...mulator-2.html

[osolemio]

Originally Posted by Clev

Don't put water on it. Ask me how I know.

How do you know?

[Piwoslaw]

Going back to the first post in this thread (see quote below) I found out that a second power plant (about 200km away) has recently started to use a heat accumulator. This one is smaller (38m tall with 21m diameter) with a volume of only 12,000 cubic meters of water, but I found that its temperature range is between 54°C and 98°C, which means that it holds about 2210 GJ of useful heat energy (if my calculations are correct). From the info I could find, the cost of this accumulator was ~$5mln.

Originally Posted by Piwoslaw

About 1-2 years ago the largest power plant in Warsaw decided to add a heat accumulator, already in use at many Skandinavian plants. It's basically a huge thermos which gets warmed up with waste heat during the day, relieving the night load. Or it can be heated at night the help generate electricity in the day. This is a VERY simple setup: just a 47m-high cylinder, 30m in diameter, holding over 30,000 cubic meters (30mln liters) of water. No extra machinery or heat exchangers, just an extra valve. Its heat capacity is 1300MW(thermal). The cost was about US$17mln. I can't find much info on it, nothing on how much it actually saves, but I did find out from an insider that the power plant is very happy with it. So much so that other plants are planning on building something similar.

EDIT: I just read that the power plant in Cracov also recently built a heat accumulator. This one has 20,000 cubic meters of water.

[Piwoslaw]

So, I bought a used heat buffer.
It is 160cm tall and 60cm diameter, giving roughly 500 liters, of which 120 liters is an internal metal tank for domestic hot water. I searched for a plumber who would redo my old heating system to install the tank, and only the seventh(!) one was brave enough to take the job.

He hooked it up, we filled it with rainwater, and... it turned out to have a leak in the internal DHW tank. NO!!!!

So I called the guy I purchased it from, he was terribly sorry, he was sure that his workers had pressure-tested it before he sold it. He promised to deliver an almost identical model, but with copper internal tank, which does not have the corrosion/leakage problems. It took many months before he found one, but finally it arrived in February


Not waiting for the plumber, I tried my luck with the connections and all seem to be good.


I put a 10cm layer of mineral wool and plastic wrap as insulation.


I filled it with rainwater and no leaks!


This week I have been slowly heating it to higher temperatures (I am approaching 60°C) and checking for issues with leaks, pressure, temperature differences between top, middle and bottom, circulation pump settings, etc.


I have not yet connected the DHW (still testing solely for household heating), but one problem that I have already identified is that I am losing heat to convection. I have a one-way valve before the boiler, so that loop is OK, but the pipe leaving the tank to the house's radiators is quite warm, and the radiators never completely cool down, even when the circulation pump has been off for hours. I was not expecting this, a plumber once told me that a stopped pump will block convection. Apparently not.

So, what to do with the convection?

1. Add some electromechanism to automatically open the hot valve when the thermostat turns the pump on, and close it otherwise,
2. Redo the plumbing to add a heat trap between the buffer and the radiators
3. Someone proposed adding a one-way valve with a spring after the pump.

I am not sure whether the spring in the one-way valve is strong enough to stop the flow, but maybe I could try both options 2)and 3)? They are more passive than option 1) so less to fail.

Any suggestions?

[JRMichler]

A simple check valve has a metal disk. The weight of that disk is probably enough to stop convection flow. I suggest just adding a check valve after the pump. I would not use a check valve with a spring because residential hydronic circulating pumps are low head pumps - they create very low pressure. The pressure needed to push the spring open will reduce flow, and could completely stop the flow.

And you are correct. A stopped centrifugal pump will not stop water flow. The water flows right through the pump.