Cavitation issues

[warno]

Ok this thread was added to alot since last i checked I'll try to get everything answered.

@maple1 my protection is doing it's job well anything over 145° the bypass side is completely shut. The bypass tube goes "cold" while burning. And i have tried many different circ speed combos. It seemed the same speed on each yielded best results. Currently I've switched boiler back to speed 2 and storage is on speed 3.

@hondaracer2oo4 I have set up an account on flat plate. That's where i sized my current HX. but not having a good idea of my flows and boiler output i was guessing, at best, at many of the numbers. The HX i settled on is the exact one from that eBay ad. It's a 20 plate at those deminions.

@Bob Rohr There's not really a good way to put coils in my boiler. Given the internal construction and internal flue HX there's a bunch of things in the way and doesn't leave alot of easy working room in there.

@Marshy my biggest concern with a much larger HX is 1) cost and 2) if boiler return temps drop below 145 then the mixing valve will be bypassing pretty often. Which i know is it's job, but if i can send 150° water back to the boiler I'd be alot happier.

 

[Marshy]

Ok this thread was added to alot since last i checked I'll try to get everything answered.

@maple1 my protection is doing it's job well anything over 145° the bypass side is completely shut. The bypass tube goes "cold" while burning. And i have tried many different circ speed combos. It seemed the same speed on each yielded best results. Currently I've switched boiler back to speed 2 and storage is on speed 3.

@hondaracer2oo4 I have set up an account on flat plate. That's where i sized my current HX. but not having a good idea of my flows and boiler output i was guessing, at best, at many of the numbers. The HX i settled on is the exact one from that eBay ad. It's a 20 plate at those deminions.

@Bob Rohr There's not really a good way to put coils in my boiler. Given the internal construction and internal flue HX there's a bunch of things in the way and doesn't leave alot of easy working room in there.

@Marshy my biggest concern with a much larger HX is 1) cost and 2) if boiler return temps drop below 145 then the mixing valve will be bypassing pretty often. Which i know is it's job, but if i can send 150° water back to the boiler I'd be alot happier.

You could buy another htx and plumb it in series instead of buying a larger one to replace it with.

I'd suggest you do this in phases. Get the inlet piping converted to 1.5" and see if you can run the pump on speed 2 without cavitating. If you think you need more heat get a second htx and plumb it in series. Let the diverter valve do it's job. To my understanding that valve is not open/shut it throttles. In the end, BTU's are going into the storage regardless if the water temp coming back. Feel free to correct me if that is bad thinking.

 

[warno]

@Marshy the thermomix valve does throttle the bypass flow, yes. But it makes some pretty bad sounds when it's at that butter zone of open vs shut on the bypass side. Thats why I just assume it keep the bypass side shut.

 

[maple1]

You could buy another htx and plumb it in series instead of buying a larger one to replace it with.

I'd suggest you do this in phases. Get the inlet piping converted to 1.5" and see if you can run the pump on speed 2 without cavitating. If you think you need more heat get a second htx and plumb it in series. Let the diverter valve do it's job. To my understanding that valve is not open/shut it throttles. In the end, BTU's are going into the storage regardless if the water temp coming back. Feel free to correct me if that is bad thinking.

That sounds sound.

I started out with a sidearm on my DHW. When I realized it wasn't getting the job done I was looking for, I added the FP in series. I also swapped my storage side 3 speed 15-58 for an Alpha, and added a B&G variable speed Ecocric on the DHW side, so I have pretty well complete variable control over flows on each side.

Warno may want to adjust the phases based on his priorities & preferences - if it is quite quick & easy for him to add a FP (vs. doing a long shut down & reman on his boiler outlet), that might be first. Or if he can or can't wait until the heating season is over.

 

[warno]

That sounds sound.

I started out with a sidearm on my DHW. When I realized it wasn't getting the job done I was looking for, I added the FP in series. I also swapped my storage side 3 speed 15-58 for an Alpha, and added a B&G variable speed Ecocric on the DHW side, so I have pretty well complete variable control over flows on each side.

Warno may want to adjust the phases based on his priorities & preferences - if it is quite quick & easy for him to add a FP (vs. doing a long shut down & reman on his boiler outlet), that might be first. Or if he can or can't wait until the heating season is over.

I can wait until this season is done. That's my plan anyway.

Can a flatplate HX be ran in series with another FPHX, Like marshy said? I've never seen it done but if i can get a 30 plate and run it with my 20 I'll do that.

 

[Marshy]

I can wait until this season is done. That's my plan anyway.

Can a flatplate HX be ran in series with another FPHX, Like marshy said? I've never seen it done but if i can get a 30 plate and run it with my 20 I'll do that.

I know your looking for someone else's concurrence but I'll just add that the only potential down side is removing too much heat from your boiler side. Maybe you can play with pump speeds to add another level of control or pipe in a small bypass on the boiler side of one of the htx's..?

You will need to plumb both sides of the htx's in series obviously.

 

[warno]

I'm not saying your wrong @Marshy, I'm sure it's been done. I've just never seen it. And I'm defiantly not ruling it out. It would just take some fancy plumbing working to achieve.


Here's a 50 plate for just under $200. Is this more what we're talking about to get by with one HX?

 

[Bob Rohr]

What size is your flat plate? Is it a 20? If so that’s tiny. Use the calculator I posted to play around but there is no draw back to oversizing your plates other then cost and you can get some cheap plates. I have a 50 plate which is feeding my primary loop on my hydro air system. No problems with the plate after 3 years. I would run a 70-100 plate hx if I was heating a water store. You can Always throttle your owb pump or tank pump to dial in th delta thst you aim for.

You will start losing some efficiency if you oversize a plate HX by too much. What happens is the channel velocity drops, you lose turbulent conditions and heat exchange diminishes. I suppose that is why they make so many sizes and have the software to select very close to what you need.

The one question still not answered is what BTU output is the boiler capable of. If you want it to run to it's best potential, the pumps, pipes, HX, etc needs to be sized to the load it needs to move. Wood boilers tend to be most efficient running full out, in gasification mode. Or completely shut off

With homemade stuff there is usually a trial and error period to dial it in.

 

[warno]

@Bob Rohr I can't tell you exactly ther output of my boiler. Best I can do is post my burn log I did a few weeks back. I can't see investing in a btu meter to only use it once or twice.

I do batch burns in my boiler and I'm getting some secondary flame but it's not as much as I'd like. Next year I'm going to change a bunch of things and aim for getting sustained secondary.

 

[Bob Rohr]

Like Karl mentioned, look at the sq ft of the HX not just the plates. That 50 plate looks like .417X 50= 20 sq ft surface.

The 10X20- 30 plate shown in an earlier post is 36 sq ft. Plus it has 1-1/2 connections and very low pressure drop even at 220,000 BTU/hr.

With the 10X20-30 and the low pressure drop, maybe go with a flat curve circ to help lessen or eliminate cavitation. Those high head, NRF- 36 high rpm circs are very prone to cavitation, and your high operating temperatures increase that potential.

If the circuit is just the boiler and HX you want a high flow, low head circulator. This Taco graph shows the differences between low and high head, the 0010 for example moves about the same gpm as a 0013, but much less head.

Taco used to build a cicc specifically for OWF, even showed the NPSH. It was an open frame motor so the issues of gunning up a wet rotor style circ were eliminated.

 

[warno]

So I was playing around with the numbers on the flatplate website. I came up with a HX that I think I find on eBay for around $200. I don't have alot of money to drop on a big name brand or custom HX. That's why I'm trying to find one I can pick up on eBay. But anyway here's one I found.

It's showing 30° delta Ts on both sides @ 10gpm. I'm guessing that that 30°delta isn't always the case of the water temps get lower. Is this correct thinking? If so what can I expect to see if I'm running 170 boiler water into the HX?

 

[maple1]

I got my B&G FP thru my local supplier for no more than I was seeing them online for.

Not sure on your local supplier situation. Mine had to order it.

Then again getting stuff online here is usually not an advantage by the time you pay for shipping & usually a currency exchange & customs etc...

 

[warno]

I got my B&G FP thru my local supplier for no more than I was seeing them online for.

Not sure on your local supplier situation. Mine had to order it.

Then again getting stuff online here is usually not an advantage by the time you pay for shipping & usually a currency exchange & customs etc...

It's not too bad getting stuff online in the states.

Here's the one I'm looking at.

 

[Bob Rohr]

Better. With the inputs you used that HX will transfer 145,991 BTU/hr. I suspect your boiler is capable of more than that, so you may need to watch how you fire it or you may still see some cycling, short run times or excessive idling.

Also you input 10 gpm on the boiler side I'd guess the circ pump, NRF 36, you are currently using is pumping more than twice that flow rate? If so the delta will decrease. Try putting 20 gpm in the A side calculation to see what happens.

If you want to pump 10- 15 gpm, which matches the HX output simulation, consider a Taco 007, a flat curve low head circulator. That would probably eliminate cavitation concerns compared to the high head NRF.

I wonder that bargain priced HX are built equal to quality name products. The weight, square footage, grade of SS, plate thickness and assembly methods are probably the big difference. Usually if it is an import knock-off they have cheapened it somehow.

 

[Marshy]

Better. With the inputs you used that HX will transfer 145,991 BTU/hr. I suspect your boiler is capable of more than that, so you may need to watch how you fire it or you may still see some cycling, short run times or excessive idling.

Also you input 10 gpm on the boiler side I'd guess the circ pump, NRF 36, you are currently using is pumping more than twice that flow rate? If so the delta will decrease. Try putting 20 gpm in the A side calculation to see what happens.

If you want to pump 10- 15 gpm, which matches the HX output simulation, consider a Taco 007, a flat curve low head circulator. That would probably eliminate cavitation concerns compared to the high head NRF.

I wonder that bargain priced HX are built equal to quality name products. The weight, square footage, grade of SS, plate thickness and assembly methods are probably the big difference. Usually if it is an import knock-off they have cheapened it somehow.

Here's the curve for his pump.

You make good points.

 

[warno]

@Bob Rohr i was just going to post what marshy did.

My current boiler side system is about 20ft of head. So if I'm reading that curve rightn it should be close to 10gpm.

And I'm sure you are right about the off brand HX efficiency. Maybe I'll step it up to a 50 plate from eBay and if need be throttle the gpm at the boiler.

 

[Marshy]

@Bob Rohr i was just going to post what marshy did.

My current boiler side system is about 20ft of head. So if I'm reading that curve rightn it should be close to 10gpm.

And I'm sure you are right about the off brand HX efficiency. Maybe I'll step it up to a 50 plate from eBay and if need be throttle the gpm at the boiler.

Sorry, I was going to correct you earlier when you started you thought you had 20' of head. Correct me if I'm wrong but, I believe you came up with that value because that's the distance between pump and htx right?

If so, that is not the correct. The best way to determine the pumps discharge head is to measure the discharge pressure before it returns into the boiler. Convert that pressure to ft of water column and find where that pressure intersects the operating curve on the graph. That will tell you how much flow its pumping.

The analytical method of figuring that out is more complicated. For every linear for of 1" pex you will have "x" feet of head loss (pressure loss expressed in units of feet of water column). You would total all the head losses in the system and subtract them from the pumps maximum discharge head and find thast point on the curve to determine flow.

 

[warno]

@Marshy I figured just under 20 ft of head for that pump with the help of another member here. We went through each fitting and gave it a length of pipe, in feet, based on online calculators for such information. So that 20 feet includes every fitting and pipe length from the boiler supply to return. We added alittle extra for any forgotten factor.

 

[TCaldwell]

I think it was jebatty?

 

[warno]

Yep that was who it was.

 

[Bob Rohr]

Basically adding all the feet of pipe and fittings gives you an equivalent length number. A few other steps are needed.

If the boiler loop side is just the wide open boiler and HX you mentioned above 10 gpm? I don't see more that a few, maybe 5' of heat? The HX spec shows the pressure drop at the flows you entered 1.1'?

Is the boiler piping undersized? 1" would be fine. 1-1/4 better if you try and move more than 12 gpm or so.

Maybe Jim was calculating the underground loop, Hx and B side?

 

[Bob Rohr]

This issue will take you through the steps to determine the pressure drop of the various circuits.

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf

 

[warno]

Basically adding all the feet of pipe and fittings gives you an equivalent length number. A few other steps are needed.

If the boiler loop side is just the wide open boiler and HX you mentioned above 10 gpm? I don't see more that a few, maybe 5' of heat? The HX spec shows the pressure drop at the flows you entered 1.1'?

Is the boiler piping undersized? 1" would be fine. 1-1/4 better if you try and move more than 12 gpm or so.

Maybe Jim was calculating the underground loop, Hx and B side?

The boiler loop runs underground into my garage. Here's pictures of everything. The boiler runs underground 22 feet of 1" thermopex into the garage then into a diverter valve - HX - and return. Everything is 1" plumbing. I know everything is messy. It's been a season of trails and errors.

 

[Bob Rohr]

Sorry, I thought the HX was at the boiler location. With this pic I can see the 20' head being realistic.

Another thought, I have seen some boilers with tube heat exchangers welded to the outside. Many of the old wood stoves had coil kits that could attach externally.

Some or the Euro boilers have a external HX like that connected to city water as the over-heat protection. If the boiler gets too hot water flows and dumps through that welded on HX.

 

[warno]

Sorry, I thought the HX was at the boiler location. With this pic I can see the 20' head being realistic.

Another thought, I have seen some boilers with tube heat exchangers welded to the outside. Many of the old wood stoves had coil kits that could attach externally.

Some or the Euro boilers have a external HX like that connected to city water as the over-heat protection. If the boiler gets too hot water flows and dumps through that welded on HX.

Any excess heat from my boiler will be dumped in the garage via dump zone water/air HX. My main concern is getting my storage up closer to 190 because my heat emitters are water to air HX built in to my duct work. And although I'm only heating the garage at the moment I've learned that anything much under 140 it takes a long time to satisfy the thermostat.