Gasification Boiler to remote storage pumping scheme Viridian pump questions....

chrisbowen

I posted this on the main board but didn't get much response. I guess it might have been more appropriate to post here so I will try again...

I want to install a gasification wood boiler in an outbuilding and run supply return lines underground to the basement with 1000 gallons of pressurized storage. I am looking at using the new Taco Veridian pumps as below. I am told by Taco however that they never completely shut off in setpoint mode but rather run at the lowest speed. That being the case, I am wondering if there are any problems in using them as below....

The boiler circ pump P1 would turn on at T1>150F (aquastat) and control T1 to 180F. The second pump, P2, which feeds storage would be on an aquastat to turn on at say T1 >180F and set to control T2 to 150F (boiler protection) so it wouldn't pump anything if the boiler was just starting or at the end of burn and not outputting 180F water...If the boiler circ overpumps and T1 drops below 180F, P2 will shut off (the aquastat) and P1 will slow down to get T1 back up to 180F. If P2 overpumps, T1 will drop below 180F and the aquastat will turn it (P2) off while P1 slows down to raise T1 back up....If P1 underpumps, T1 will exceed 180F and it (P1) will then speed up to control to 180F. If P2 underpumps, T1 will increase and T2 will increase, causing possibly both P1 and P2 to speed up....It would seem though that under pumping is not an issue with these pumps , but rather the possibility of over pumping since they don't shut off. In my application, it seems to me, and I could have this wrong, that over pumping wouldn't be a problem...???

At the start of the burn, P1 and P2 would be speeding up to keep up with the boiler BTU production, reach peak speed, then start slowing down with the decrease in heat out....

The goal of this design is to supply a steady 180F to storage. Return from storage will be at a steady 100F.

Any comments? Thanks in advance.

Ironman

I'm not sure that the Viridian circ will operate as you describe:
Pl on at 150, set point 190. The circ will be pumping full speed at 150 and slow down as it approaches 190. How will it then slow more as T1 drops? Are you confusing make on rise with make on fall or am I missing something?

Who taught you to spell BOAN that way?

hot_rod

Not sure why you only want to circulate when the boiler is at 180F. The lower the boiler operating temperature the more efficient, and start transferring that energy as soon as the boiler is above the storage tank temperature. VS circ pumps can handle the return protection.

Did you have a chance to read through the Biomass training link I posted in then other thread? It clearly explains piping, pumping and wiring options for what you are trying to accomplish.

chrisbowen

The Viridian has a cooling setpoint mode, which Taco use to call "reverse acting" so the pump will indeed work as I have indicated (it will need a resistor in line with the sensor to change the control range from 100F to 180F). It will speed up with rising temp and slow down with decreasing temps.

Yes, thank you for the link to the Siggy material. I have his book and have read all of the info.

I want to control the boiler outlet to a steady outlet temperature, say 180F, to charge storage in a one and done cycle. The water in the storage will all be at 100F when the boiler fires. Water will hit the boiler loop at 100F and return to storage at 180F. The 100F water in storage is replaced with 180F water, until all of the 100F water is at 180F. There will be no recycling of water from the tank back and forth through the boiler this way. The large delta T allows for smaller flows which means smaller pumps, smaller piping, less electricity.

Zman

I am not sure I understand where you are heading.
The storage tank needs to absorb approx 640k/btu. Unless you have a ridiculously large gasifier, it will take several hours to generate that much energy.
Some mixing is going to occur in the storage tank. There is no "one and done" . You can't just pull out a gallon of 100 degree water and replace it with a gallon of 180 degree water.
Even if both circs are using 50 watts, that is only a penny an hour.
Maybe I am missing something but I would do it Siggy's way.
Carl

chrisbowen

The boiler holds about 90 lbs of wood. Figuring 6000 btu/lbs and a 75% efficiency, that is about 400,000 btus into the tank from one charge. It will probably take 1.5 loads to completely heat the tank. The average burn time of this boiler with a full load is between 2 and 3 hours, so it will take about 4-5 hours to accomplish. With the heat loss of the house, the boiler will have to be cycled once a day during subzero temps, perhaps every other day when temps are warmer.

If care is taken to ensure the temps can stratify in the tank, one and done should be doable. I know someone who is doing this very thing and he claims it works very well....

Zman

Please report back with results. I am interested...

chrisbowen

I will once I get the pumping figured out and get things together....Thanks...

chrisbowen

I talked with the Viridian product manager today (thanks Doug!) and he tells me that actually, the pump goes into a sleep like mode when the set point is reached, rather than continuing to pump at low speed. Excellent!

Harvey Ramer

What is the BTU output of your boiler?

chrisbowen

It's rated at 200,000BTU/hr

Harvey Ramer

You are looking at the new VR1816 ?

I wouldn't be comfortable with a circ that small. On a gasifier I typically size the circ figuring about a 15-20 degree delta tee. For a gasifier to be efficient, it has to be gasifing. Which means you have to remove the BTU's as fast as it makes them till your burn is complete. When your tank is in the loading process, you will start seeing some higher return temps, at which point you either have to move the water or the boiler will start cycling on high limit.

chrisbowen

I'm looking at the VT2218. I will only be moving about 5-6gpm at max boiler output to storage. The key is the delta T, which is about 80-90F and good stratification. About 12-15gpm through the boiler with a 30F dT....

Harvey Ramer

Well, it should work as long as you can get the tank to properly stratisfy.

chrisbowen

It is reportedly working very well for one person I have talked with though he is using an on/off control on his pumps. I would rather use the Viridians as it seems a more elegant solution...

Undoubtedly, I want the system to be stratisfied!

Weezbo

http://www.caleffi.com/usa/en-us/catalogue/thermobloctm-recirculation-and-distribution-unit-npt-281165a soory about misdirecting you to the idronics 15 and 16 . this unit is like the Landomat. it works like the mixer that allows circulation when 140 F is reached ...the reasoning behind this is the variations in wood and moisture content tend to make cresote build up more likely unless the boiler has some sort of boiler return temp protection.
i really want this to work for you , so take a look at the thermobloc.

sfcdavidamccoy

I know this is an old link, but I'm wondering if and how the Taco Viridian pumps worked out with your wood gasification boiler? I'm using a 3 speed grundfos to supply my hydronic storage. I have to change the speeds depending on how hot my fire is. I'm wondering if I could put a Taco Viridian in it's place, set to a certain temp and the pump would speed up or slow down in order to maintain a certain temperature?

I'm not an expert by any means and if I'm using this completely out of context I'm apologize upfront.

hot_rod

Like this it will work, the setpoint controlled circ becomes the thermal clutch or disconnect. It takes heat from the boiler at the rate the boiler can produce it.

skalor

sfcdavidamccoy said:

I know this is an old link, but I'm wondering if and how the Taco Viridian pumps worked out with your wood gasification boiler? I'm using a 3 speed grundfos to supply my hydronic storage. I have to change the speeds depending on how hot my fire is. I'm wondering if I could put a Taco Viridian in it's place, set to a certain temp and the pump would speed up or slow down in order to maintain a certain temperature? I'm not an expert by any means and if I'm using this completely out of context I'm apologize upfront.

I have a 60k btu pellet boiler I've been using the VT2218 on since 2017. I run in delta T with the delta setting at 10°. It's charging a 120 gallon buffer tank that is the primary loop and the secondary loop is the zones that are run off the tank. I don't have any thermal protection on it but if the tank drops below 130° a gas boiler run in parallel charges the tank back to 160°. Pellet boiler has outdoor reset so buffer temp varies from 150°-180° depending on outside air temp. Definitely think this is the right product for you if you are constantly changing the speeds. The circulator will vary the speed to maintain the delta T so at low output it will run slow and high output it will speed up.