When to fire for efficient storage?

[VeggieFarmer]

VtRv: are you running a radiant system to heat the house? I've been experiencing heat loss similar to yours - losing between 3 and 4 degrees F per hour from the storage tank when the outside temp is roughly 32F - and believe it is due to the way the radiant manifold operates. Since the goal of a radiant system is to pump low-temperature water continuously, I have a circulator that is constantly running and drawing heat from the tank. In fact, two circulators: the first provides a loop of tank-temp water into a four-way mixing valve while the second takes the water from the mixing valve and sends it through the manifold and the house. The first loop is at whatever temperature the tank is (typically 120 to 150 F) while the second is at whatever temperature the radiant requires (typically 95 to 110 at this time of year.) It's hard to sort out how much of this heat is genuinely needed by the house and how much is being lost to the inefficient plumbing design, but the upshot is that I'm on track to burn 9 cords of wood this winter even though my square feet of heated space is similar to NoFo's.

NoFo: I'm plagued by what seems to be an overly aggressive inlet protection valve. When the Eko has run for several hours and is up to temperature (typically in the 73 to 81 C range on the controller), the temperature going into the storage tank is about 3 C lower. This makes it impossible to raise the storage tank temperature much above about 65 C, or 155 F, since a temperature differential is required across the heat exchangers (copper coils in an SSTS tank.) If I close off the bypass to prevent the inlet protection valve from being able to mix, I can drive the temperature at the boiler into the mid 80s and at the storage tank inlet up to the upper 70s, but the controller idles the fan alot since the flow to the tank is constricted by the still-partially-closed thermostatic protection valve. Is this just the cost of doing business with an inlet protection valve, or is this a malfunction? (It's a Danfoss ESBE valve.)

Somewhat off topic, though related to the previous posts....

 

[Fred61]

Veggie,

I don't want to sound dumb and I don't want to question your intelligence which, I'm sure exceeds mine, but I'm going to ask: Do you have the circulator on th correct side of the bypass?

 

[VeggieFarmer]

Veggie,

I don't want to sound dumb and I don't want to question your intelligence which, I'm sure exceeds mine, but I'm going to ask: Do you have the circulator on th correct side of the bypass?

No offense taken on either count. The circ. is on the return side, just upstream from the boiler, with the thermostatic bypass just upstream from that. The plumbing appears to be all in order, with the inlets to the valve (one from the tank return, one from the boiler supply) as diagrammed. Unlike the Termovar, this Danfoss valve does not have integral shutoff valves.

 

[stee6043]

Medman just had several posts regarding his Danfoss valve being sent to him "backwards". That is, his diagram showed the installation being backwards from what his thermostat actually was. You may want to crack open the cover on your valve and confirm that the thermostat is indeed pointing the right direction, regardless of what the sticker on your valve indicates.

 

[Nofossil]

Medman just had several posts regarding his Danfoss valve being sent to him "backwards". That is, his diagram showed the installation being backwards from what his thermostat actually was. You may want to crack open the cover on your valve and confirm that the thermostat is indeed pointing the right direction, regardless of what the sticker on your valve indicates.

Good call - that might explain it. It's also possible that the Danfoss has an element that's at too high a temperature. I read somewhere of one that opened at 165 degrees. Unless you're burning really green wood, I expect that 130 is hot enough to provide protection.

Basically, if your return water (before the Danfoss) is less than 160 degrees and the boiler is idling, there's a flow problem.

 

[Fred61]

I may be missing something here but I don't see how you could have even partial success with the valve backwards.

What happens when you just restrict the flow through the bypass instead of shutting it completely? Could be the return water would take the path of least resistance.

It is my understsnding that the higher temp thermoststs (165 degrees) are available for those who want to place the valve on the output side and the 140 for the return side

 

[VtRv]

Veggie- I don't have any radiant heat. It's all baseboard hot water and a Superstore for my DHW.

 

[cguida]

I am new to the water tank stored heat game, and am still finding out how it interacts with my boiler (Memco) and wood supply (junk blow-down Spruce and Fir and Cedar).

Basically, we just get up in the morning, and keep the boiler stoked up while we are in the area. The house is pretty much on its own during the day. Then around 4 or 5pm, we stoke it up again, and keep it that way till bedtime. A load of junk wood lasts less than 2 hours. We get the tank up to about 170, and after the last junk wood fire goes out, it's up to the tank. In the morning so far, the tank temperature is between 150 -160, and we start all over again. So far, it all seems to be working out well. Not having to always be on top of the fire (junk wood...) is a real luxury.

We find that we can raise the tank temperature at a rate of about 2.5 degrees/hour with a good hot fire. Does this seem about right?

I wonder sometimes if we could raise the temperature of the tank faster if we let it run down more. I think the flat plate heat exchangers work better if there is a larger temperature difference. So if the tank were down around 130, and the boiler was north of 170 -- that might make for a faster heat transfer. But so far it is all working out with tank temperatures between 150 -170.

Am I correct in understanding that it is not a good idea to heat an EPDM(?) tank hotter than about 185? What will happen if it gets hotter than that?

On a related (but different subject), does anyone have experience with the Dallas Semiconductor DS1620 digital thermometer/thermostat IC? Seems like alot of 'functionality' for 6 bucks at Jameco.
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2735

 

[Nofossil]

Medman just had several posts regarding his Danfoss valve being sent to him "backwards". That is, his diagram showed the installation being backwards from what his thermostat actually was. You may want to crack open the cover on your valve and confirm that the thermostat is indeed pointing the right direction, regardless of what the sticker on your valve indicates.

Good call - that might explain it. It's also possible that the Danfoss has an element that's at too high a temperature. I read somewhere of one that opened at 165 degrees. Unless you're burning really green wood, I expect that 130 is hot enough to provide protection.

Basically, if your return water (before the Danfoss) is less than 160 degrees and the boiler is idling, there's a flow problem.

 

[in hot water]

the wider the delta t thee more energy you can store, or use. If possible run the tank to 180, 190 or thereabouts, and pull it down as low as possible to cover the load. Radiant floors are about the lowest temperature emitters. Radiant walls and ceilings close. Panel radiators can work down around 110- 120 if you size them correctly. Figure 130 ish for baseboard.

Pull the tank even lower buy running it through a DHW preheat tank, lastly. If your well water is 50F, you may pull the tank down to 70F. Now you have a great delta t to leverage 70- 190! Now you present the boiler with an ideal load to keep it running hard and at peak efficiencies (non stop)

You will notice how quickly the tank temperature rises when starting from cold, say 70F temperatures. As the boiler gets the tank to within 5- 10 delta t the transfer slows. Seems that last 10 degrees takes as long as the first 50 This is where you will see the boiler bounce off it's limit, cycling off more frequantly even though the call for heat still is there.

Mixing valves or circs running on outdoor reset curves really shine, for this application. They allow the storage to be pulled to the lowest possible temperature every time, based on the outdoor temperature and building loads. Sort of a heating cruise control, matching load to hp.

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