How Should a ModCon Boiler Use a 1/25 hp ECM Pump with 160 Gallon 4-Coil Solar Assist Storage Tank?

TCTOPPS

This question pertains to how to utilize a pump. I have solar assist. I am using a modcon combination boiler with emitters.

I have two 80 gallon tanks that I was thinking of hooking up in series. They each have 2 heat exchange coils. I was planning on using the lower two on each tank for the solar loop and the top two for dhw water to a combination modcon boiler. The 160 gallons I was going to run thru 4 baseboard emitters. The tanks are in a full basement. Three of the home run loops are up 1/2 floor. (See later post for updated schematic on coil and tank use.)

I wanted to push the water mass from the cooler storage tank with a Delta P pump to the hot tank and take out of top to the modcon combination. The way I was thinking included placing the Delta P pump with check valve at the return into the bottom of the cooler tank. (See later post for updated circulation post.)

I was looking for the best combination of storage and HX use. If I can not easily push that water, then I would have to probably supply and return via the tops of the tanks.

The other would of course be to change the use of the top two coils and use the storage mass for dhw.

What do you guys think? I have experience in water pumps with equipment use and general plumbing.

I know the Delta P can be used for emitters thru a loop. But how about the lifting of this water volume???

Thanks for your input!

TCTOPPS

Are the tanks the same as a column of water in that they would require the pump to be much more powerful?

Rich_49

Could you draw a picture of what you want to do ?

SuperJ

A picture would help. But I suspect a carefully balanced reverse return parallel setup would work better with less complication than a series arrangement. It sounds like you have a mod con combo boiler and are using an indirect setup?
How much contribution will the Solar make?

You could put the solar into the bottom coil. Boiler direct into the mass and reverse indirect heat your dhw off the top coil. But that would require keeping your mass at maybe an efficient temp for your boiler if your solar isn’t carrying the load.

Jamie Hall

If this is a closed loop -- and it sounds as though it is -- you aren't lifting the column of water at all. All you have to do with the pump is overcome the friction loss in the pipes, assuming that the static pressure in the loop is high enough to keep the pipes full.

So, since you say you have experience with pumps -- look up the pump's characteristic curve at full speed and figure up the friction loss in your piping, and where they intersect -- as usual -- is the maximum flow a variable speed pump will pump.

GroundUp

What size, length, and type of pipe? How many elbows? As Jamie stated, in a closed loop you aren't really lifting anything so much as circulating it. What goes up must also come down which cancels the head accumulated in a column

SuperJ

The technical guide has a lot of good info and shows some ways for connecting multiple thermal storage tanks together. https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

hot_rod

The coils in the tank would need to be copper or stainless to run DHW thru them.



3 or so ways to pipe and control multiple solar tanks.To drive the best efficiency out of the solar you want the coldest possible water going up, so pull the solar from the lower coil, lower connections.

Here is a reverse return on the tanks for hydronic, solar coils looped as one, domestic coils in series.
Depending on what type of coils are in the tank and pressure drop of them?

With the Caleffi BX and MX lite controller you have three different ways to load tanks. You can do like this drawing.
Or split the tanks and prioritize one, the DHW typically is loaded first, any additional solar goes to the hydronic tank.
Or step load them, take one to 100f, then the second, then tank 1 to 120f, then the second. The step loading tries to maximize the solar by running the coldest possible fluid to them, l,loading in steps does that but DHW may not reach setpoint on low solar gain days.

You need to pipe the tanks according to which loading logic you chose.

Not sure how you want the boiler to interact for heating? When the tanks drop to a low setpoint?

TCTOPPS

@Rich @SuperJ @GroundUp @Zman @Rich @SuperJ @Jamie Hall @hot rod
Wow! Your answers are a lot of info to consume in one setting! I appreciate your feed back to help solidify my thinking.

Here is the history of my thinking and the info on the original system from 30 years ago.

The original question had to do with the pump operation, its selection and how to push the water thru the storage tanks using the mass storage as a loop. (As a result of your responses I am reconsidering different coil and tank arrangements.)

The two tanks are commercial tanks each having two copper coils within stainless steel tanks. The length of the home runs on four emitter loops in total are about 450' with each loop 190/150/80/30 feet. --1/2 inch PEX

(The solar drain-back tank to panels is a separate loop. The food grade glycol affluent from panels drain back to a small 20 gal tank, then from there it gravity feeds the lower solar HX coils in tanks. It is then recirculated back to panels with a new self automated Taco variable 'solar series' Delta T pump 009. The lower 2 tank coils are hooked in series prior to this pump sending affluent to complete the HX loop back to solar panels. All of which is proven technology.)

(The modcon boiler is a HTP combination boiler 140,000 BTU 'Floor Unit' with a small approx. 3 gallon buffer tank. (Westinghouse has the exact model under its name at great pricing.) It has many control features included that I would need to wire separately 30 years ago. The boiler will heat stand alone or with solar assisted water to space heating emitter loops and/or DHW separately on isolated loops.)

(Originally the house in Minnesota was sized for 80-90% DHW and 40% space heating. Since its original install in 1982 we have added exterior insulation, wrapped the house, put in e-glass windows and installed a very high efficiency forced air furnace. I have 6 Morning Star panels from AET that are still usable. (AET is still in business!!!) 2 panels is usually enough to handle a 4 user family home for DHW with a 80 gallon tank at 80% 'approximate' of demand. We are currently a 2 user family.)

(We had Grundfos 1 speed and 3 speed circs back then. The space heat HX was a radiator style into furnace plenum from a tank coil. I may add again the same to the forced air furnace; but first want more comfort in the 1/2 basement hence the baseboard emitters.)

So all around I expect additional efficiency with the insulation, heating and pumping systems.

I still do not clearly understand if the 1/25HP Delta P pump would be adequate for pushing water through the storage side of the 160 gallon tanks in conjunction with the 450 foot emitter runs!!!

Because of your suggestions I am reconsidering the tank / coil arrangement. These ideas would loose my concern for the 1/25 HP Delta P pump.

1) I like parallel tank arrangement as it would even out temperatures and BTU availability between tanks. In this scenario solar HX coils in series lower tanks. The two remaining would be one coil on top hot tank for dhw and the other if slightly cooler tank would feed boiler. This idea seems to be wasteful of the mass storage as it would be static non-potable water and not used as a loop. (Original question was on this point of the Delta P pump use of the 160 gallon tank as its own loop with the modcon and emitters.)

2) By isolating the mass water storage of the tanks, I could use the hotter 80 gallon storage for DHW. I would use the upper loops for solar assist to modcon and emitters using the Delta P pump. I like this idea maybe more. This would give more 'time in two coils' for BTU recovery in the heating loop while still maintaining higher BTU availability to DHW during peak solar activity. The second storage tank would be static and completely isolated yet stage preheating for solar assist to modcon emitter heating loop. (I could access this static storage for other applications at a later date.)

3) Make the 160 gallon mass water storage in the tanks as static and hence not potable.

I expect to operate the boiler at as low a temperature as possible. I think 120 degrees to the emitters back to upper coil in cooler tank if doing this arrangement with Delta P pump.

I would simply have an 'on' switch at modcon location or from thermostat fan control. When selected it could use a relay to operate continuously the variable speed Delta P pump at heating season. TVR's would handle the comfort level at each emitter. The boiler would operate as per factory spec and do its own thing using out door reset and summer shut down.

Some people think this modcon does not need a thermostatic control as it is its own self contained appliance??? What do you think? Is continuous 'pump on' a feature of a modcon if selected? It is with our forced air furnace???

I ask because Delta P pumps do not like being repeatedly turned on and off. How would you handle this question for control of Delta P pump with modcon. The modcon has I believe a 1 minute to 60 minute range post heating cycle timer to run a pump. I do not understand this feature. Can you explain please?

I was intrigued by the 160 gallon tank mass storage as the feed for the boiler since I am using TRV's on emitters.

So what conclusions do you make of these ideas? I am liking #2 as best possible. Is my original idea workable? Would it require a bigger pump?

I know this is long. But I wanted to clarify a couple questions you created in your responses.

Thanks again, I appreciate the feed back.

Jamie Hall

May I presume that the proposed piping has the 1/25 hp pump pumping through 450 feet of half inch PEX, plus coils in the storage tanks? Or is it that 450 fool loop drawing from the storage tank itself, to the pump, then into the loop and back to the tank. In the former case, you need to figure the head loss in the PEX (be sure to include fittings and valves) plus the head loss in the storage tank coils and see where that falls on the pump's characteristic curve -- that will be your maximum flow. The latter case is the same, but you don't have the loss in the storage tank coils to worry about.

The mass or volume of water in the storage tank is completely irrelevant.

Without the pump curve it's not possible to say whether it will work or not.

TCTOPPS

@hot rod If I understand you correctly the solar coils are at the bottom two coils hooked in parallel. The mass storage is used to circulate thru modcon and emitters. The top two coils are hooked in series potable cold water in and hot to the combi boiler. I guess my question is will a 1/25th hp on bottom of ttank handle this?

I would go into bottom of tank with return from emitters and out the top to the modcon. (I have two ports at top. I also have two available on sides. Why out the top?

The boiler would come on as usual when tank temperature falls below set point.

Thanks!

TCTOPPS

@SuperJ Thanks for the reading material. Good info!

Zman

@TCTOPPS
The horsepower of the pump is not all that important. It's pump curve is. What model pump?

Jamie Hall

Zman said:

@TCTOPPS
The horsepower of the pump is not all that important. It's pump curve is. What model pump?

I keep asking that...

hot_rod

Before you spend a lot of time and money on the system... If one goal is to use solar thermal for a % of the heating load, 4 collectors in a cold Minnesota sky will probably provide less that 50,000 BTU PER DAY! not per hour
So don't spend a lot of $$ chasing that energy. The collectors are fine for DHW loads, leave it at that.

Why glycol in a drainback?

Here is the performance data for an AET 4X10 collector. For heating use condition C or D, depending on what temperature you are looking for.

In the right column notice the output under 3 different sun conditions. On a medium radiation day, condition D, expect 13,000 BTU per day per collector. So maybe an hours worth of energy, from 4- 4X10 collectors? IF the sun shines for 6 hours.

I'd suggest 10- 12 collectors minimum for considering any sort of heating application.

Really the only viable solar heating in that climate is passive, let the sun shine in the window, cheap and low tech. Unless you have unlimited $$? You don't get enough sun and it's too cold outside to recover much of what the sun can deliver.

TCTOPPS

@ZMan A Viridian Infinitely Variable ECM High Efficiency Circulator, Less Flanges - Universal (120V) pump! It is a Delta P Pump capable.

Or a B&G Vario Constant Curve Eco Circulator Pump 6050B2003

TCTOPPS

@hot rod 6 Panels! This is a retrofit of a previous system with new tanks for dhw and space heat assist. The panels are the only thing remaining from 30 year old system.

Why glycol? Good Question! Things freeze up in Minnesota! Chuckle!

We have a more than decent exposure to the sun here; but hey it's not Florida.

I have very good drainage back to tank! I do not want to take a chance with a dead spot that could freeze with water. I want a more simple and easy to manage solar side of the equation.

Antifreeze in a drain-back in Minnesota is in my opinion best suited for use by the non-tech types who want to turn on system and basically forget it sans a yearly system checkout.

I am seeing 13,000 per square foot per day x 40 square foot looking at the pdf. That would be 52,000 per panel x 6 qty equals 312,000 available btu's on an 'average' day.

Those 6 panels have got the water up to 200 degrees quickly in the former 240 gallon tank during the Summer and shoulder months. I am setting tank temps for around 160 degrees.

TCTOPPS

@GroundUp As as far as piping the emitters are 3/4" and PEX will be 1/2". Total length of 4 home runs will be approx. 450' with very gradual bends and only two - 3/4" 90 degree elbows at corner of rooms. Emitter lengths are 62 feet total. 388' of actual PEX piping. 3/4' PEX will be used to join emitters at at 90 degree elbows.

hot_rod

> @TCTOPPS said:
> Hot Rod; 6 Panels! This is a retrofit of a previous system with new tanks for dhw and space heat assist. The panels are the only thing remaining from 30 year old system.
>
> Why glycol? Good Question! Things freeze up in Minnesota! Chuckle!
>
> We have a more than decent exposure to the sun here; but hey it's not Florida.
>
> I have very good drainage back to tank! I do not want to take a chance with a dead spot that could freeze with water. I want a more simple and easy to manage solar side of the equation.
>
> Antifreeze in a drain-back in Minnesota is in my opinion best suited for use by the non-tech types who want to turn on system and basically forget it sans a yearly system checkout.
>
> I am seeing 13,000 per square foot per day x 40 square foot looking at the pdf. That would be 52,000 per panel x 6 qty equals 312,000 available btu's on an 'average' day.
>
> Those 6 panels have got the water up to 200 degrees quickly in the former 240 gallon tank during the Summer and shoulder months. I am setting tank temps for around 160 degrees.

13,000 per panel per day, not per square foot. A solar day is about 6 hours, maybe less in winter

and that is a 4X10 40 sq. foot AET providing about 100 degree temperature. Can you use that low of a temperature in your system?

TCTOPPS

@Rich @SuperJ @GroundUp @Zman @Rich @SuperJ @Jamie Hall @hot rod
Okay, I got some spare time to dig this info up. Does this help in the discussion?

550ft length (450 ft plus 100 ft coil) x .03 of head is 16.5 head plus 2.0 additional for a margin is 18.5 head

I am figuring 40,000 btu's total load for 4 basement areas loops at 10,000 btu per home run. I am assuming 1 gallon flow / minute to achieve 10,000btu / hour for each loop. (The entire house heat loss was figured at 80,000 30 years ago.)
---------------
18.5 head x .434 for each 1ft of head = 9.09 psi ???
restated
7.812 psi x 2.3 ft of head/ft of head = 17.97 head ???

(1 psi = 2/3ft of head)
(1 ft of head = .434 psi)
-----------------------
So 1 gallon per minute for each loop approx.

The listed pump VR1816 and Vario Constant Curve Eco from B&G with ever so slightly more capability would both be at the very high limits of their numbers. They handle the gal per minute but not the head requirements at 4 gal per minute.

The 3452 only puts it at the middle of its curve and easily handles this load.

All three easily handle the psi requirement.

Am I correct?

Thank you for your time!
------------
Viridian VR1816
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Taco-VR1816-HY2-4C2A00-Product-Overview.pdf
------------------
Vario Constant Curve Eco
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Bell-Gossett-6050B2003-Brochure.pdf
---------------
and Viridian 3452
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Taco-VR3452-HY1-FC1A00-Product-Overview.pdf

SuperJ

To me that VR3452 is way oversized for your application, but it has some nice features especially with that add on control module allowing 0-10v control etc. It looks like it has a infinitely adjustable max pressure point for the PP curve but I'm not sure if it learns to apply that pressure at a specific GPM. (18fthd at 4gpm seems kinda high for your 40kbtu load.)
My pick almost was the VR1816 (assuming your correct in 4gpm@18fthd) it has the right area under the curve as a nice feature set. It looks about right, but when I looked at the proportional (and constant) pressure curves the highest setting wasn't high enough (only 12fthd at 4gpm on highest PP curve).

The BG 6050B2000 looks like it matches perfectly when you select auto curve 7. I suspect in the real world you might find you could go down a notch or two on the proportional pressure curves. Make sure you get the proportional pressure model though, not the constant curve if you're using TRVs. A downside to that pump is that it's as flexible in it's options. You have to order it either as constant curve, or proportional pressure. But getting the right pump for the application is more important than a feature set you won't use.

You want the

SuperJ

I suspect the Grundfos Alpha2 would work as well on AutoAdapt (proprietary proportional pressure algorithm). It's slightly low on pressure but I think your pressure drop calc is a little on the high side.
https://us.grundfos.com/content/dam/NAMREG/Literature/ProductFlyer/LALSL002-ALPHA2-0217.pdf

Zman

You don't want to add up all the loops to determine your resistance. Generally, if you take the longest loop and use that value, it works pretty well. In your case, you will want to balance the short loops or they will take much of the flow.

SuperJ

I reread some of your pressure drop specs. It's unclear to me if you have a total of 450ft of .5" pex in series or if you have 450x4 (in parallel for each circuit), or if you have a bunch of parallel circuits totally to 450' (what I think you have based on some comments). If you can post a diagram (even a rough hand drawn one) with tubing sizes and lengths, with all your components that would clarify things and avoid bad assumptions.

Base on your comment The length of the home runs on four emitter loops in total are about 450' with each loop 190/150/80/30 feet. --1/2 inch PEX it looks your longest run is less than 200'.

This means your total pressure drop is substantially less than 18fthd, assuming your circuits each have a dedicated 0.5" pex supply and return run. You might be closer to +/-10fthd, which is a sweet spot of the VR1816(PPHigh), BG 6050B2000(auto4 curve) or Alpha2 (autoadapt) pumps at 4gpm.

TCTOPPS

@SuperJ The B&G pump 6050B2003 replaces the older models Vario Constant 6050B2001 and Auto Proportional 6050B2000.

It looks like they have combined the two pumps into one ...the 6050B2003.

The 4 home runs total 450' plus 100' coil. All 1/2" PEX minus 62' length of 3/4" emitters. Yes, 190/150/80/30 are the different home runs.

TCTOPPS

@Rich @SuperJ @GroundUp @Zman @Rich @SuperJ @Jamie Hall @hot rod
I want to use this control from Taco for the Delta P pump:
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https://www.supplyhouse.com/Taco-SR501-OR-4-FuelMizer-SR501-OR-4-Switching-Relay-with-Outdoor-Reset
-------------------
The Taco tech says to wire it in parallel with out door switch to turn off Boiler and Pump at the same time with Summer time temperature limit.... Would I need to disconnect (boiler ODR) and replace the one that comes with the boiler? He said that I could use the same sensor for both. Would both ODR use the same sensor???

SuperJ

For your flow calc simply sum the parallel circuits.
For the feet of head, take the worst case circuit on it's own @1 GPM, and then add to the pressure drop of your common piping @ 4gpm.

Some ECM pumps (like the Grundfos) don't require a control to shut it off, but you can manually switch it to a summer mode (exercises the pump occasionally). Some can handle temporary deadheading. The pump can tell it's not moving any water and will basically wait and keep checking for a valve to be open by occasionally speeding up and sensing if there is any flow.

Zman

Here are the flow calcs for your loop lengths using the Grunfos 15-58 (same curves as the alpha) at high and low settings.
You can use the head loss numbers on the left to simulate performance of different circs in your system. If you post the curves of the circs you are considering, someone can help you compare.

SuperJ

You may want a balancing device on the shorter circuits to even out the flow.

TCTOPPS

@SuperJ I think a TRV would do the balancing??? What does 'sum the parallel circuits mean???

SuperJ

@Zman 's post shows a correct pressure drop calc using software. Look at his diagrams and see if they kinda match your system. Even with TRVs you often want to balance, otherwise flow tends to take the path of least resistance, and you will get wastefully high return water temperatures. It's true the TRVs will regulate space temperature without balancing, but to get top efficiency and performance in all conditions you need to balance. Sometimes balancing is just throttling a ball valve and marking it with a sharpie marker.

An example would be if the TRV is wide open on a short run it will take over 3GPM (depending on your circulator) there might not be enough pressure to left to get design flow in the other circuits. Or you might end up over pumping because of lack of balancing.

TCTOPPS

Here is another computational help.
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http://spacepak.com/modules/news/upload/{7C28944F-EA07-4E17-B21B-79B37040FA07}_water_works.pdf
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TCTOPPS

@hot rod

Yes, I can set the boiler lower than 120 degrees supply. I recall the lowest setting at about 90 degrees with an adjustable range of up to 27 degrees less for the inlet difference.

Solar panels at 1500 btu per square foot per day is what they create. They however transfer less for actual application. So in colder climate 60,000 btu's are transferred for use at 13,000 btu's per day. Is this what you are referring too? (1500 sq ft squared per day X a coefficient = 13000.) Then the six panels would make available approximately 78,000 BTU's!

It is not always below zero here in Minneapolis / St. Paul. We do not expect much production in the coldest weather except for DHW. It is the shoulder months that I expect solar assist for space heat.

Here there are about 10 days that consume a huge percentage of fuel versus the entire heating season.

We could also create a larger heavily insulated ground heat sink for storage prior to shoulder months in the floor of an addition. What do you think of this idea?

In years past the panels would make some really hot DHW water with previous tank. Such that DHW system 'must' use a mixing valve. It is that hot. I shortened the life of some of the components (the tank) with 180 to 190 degree temperatures. Today stainless steel tanks are great compared to what my installer designed for me 30 years ago.

I am still confused on the correct pump.

Thanks!

TCTOPPS

@SuperJ
The loops including the returns are 450' 1/2 pex pipe.

TCTOPPS

@Zman
I looked at the screen shots. Are you figuring the four home runs? What is the difference of the Grunfos vs Taco vs B&G as far as the operation of them? I am looking at Delta P pumps.

TCTOPPS

@Zman
Are you saying to just use the information off of the longest loop to do the computation?

Zman

If you use @TCTOPPS they get a message that you are trying to get there attention.

The software models the performance of all the loops. I put in the 4 lengths you are using and it shows what the flow rates will be. The software is older and does not include some of the newer circs. It is still useful because you can create the system curve and apply it to any circ.

Anyhow, I think all the major brands make a delta P circ that would work well in your system. What brand do you prefer?

As @SuperJ mentioned, you really should balance the loops so you get even flow. These are a nice, easy solution https://www.supplyhouse.com/Caleffi-132432A-1-2-NPT-QuickSetter-Balancing-Valve-w-Flow-Meter

TCTOPPS

@Rich @SuperJ @GroundUp @Zman @Rich @SuperJ @Jamie Hall @hot rod
Here is a quick schematic.
---------------

-----------
and
-----------------

-----------------
and Westinghouse / HTP boiler


--------------------
and Full Brochure

http://www.westinghousewaterheating.com/literature/WH-Combination-Heat-Hotwater-Floor-Brochure.pdf

Rich_49

Do you already have these tanks ?

Are you sure you can procure this combi you have shown ? It is discontinued , It was the HTP EFTC140F . If you can get it , do it fast , the newer model has no internal circ for DHW because they have switched to a 3 way valve .

TCTOPPS

@Rich this is a Westinghouse re-brand. Exact same system as it was explained to me by tech??? The brochure came from the Westinghouse site same manuals as HTP. All nomenclature that I have seen includes the buffer tank in the floor model. This model has a circ with the boiler to the indirect tank. There is a coil in tank that leads to an electronic mixing valve for dhw outlet temperatures. What would the three way valve you refer be used for in system?

The system also has a 2nd central heating pump? What do you think is the use for this pump?

Tanks? As to solar tanks, yes, two 80 gal stainless with 2 each 1/2" copper coils. I am debating with best connection combinations. Isolating tanks, series or parallel solar loop, mass storage for a loop to solar assist boiler in the emitter loop among others.

What are your thoughts on tank arrangement and a Delta P pump.

In Minnesota on an 'average' winter day approximately 78,000 usable BTU's from 6 AET flat plate collectors. So space heat assist will be 'most' effective in shoulder months while getting adequate in winter if not superior DHW assist through out remainder of year.

Thanks

hot_rod

This Idronics 6 issue takes you through the steps to designing a solar combi system.

A few key points, using the lowest possible temperature emitters, storage, and separate solar tanks as opposed to combi tanks to maximize solar harvest. You want to present the coldest possible tank to the solar when the sun comes up every day.

The Syracuse example is probably close to what you might expect in your area for solar harvest, the bar graph shows what is available.
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_6_0.pdf

A solar simulation program, I use T-sol would give you exact data for your system, location, and realistic expectations for solar portion. They may still have a free demo version online to crunch some numbers.

Here is a small DHW solar in Alaska. Notice max. collector temperate and % of contribution in winter months. Obviously AK would be different than MN for winter solar But the program graphs based on weather station you input.

RET Screen is a free simulation program for energy calculation.