Fixing problem w/ indirect water heater

bill nichols

A friend of mine just had an addition put on his house and installed a new 150 MBH gas, hw boiler, and a 40 gal Bradford White indirect water heater (M2-P-40R10). The heat works fine (1 zone fan coil, 1 zone BB), but the 3rd zone (3/4" zone valve) is the water heater, and there is less hot water that his previous standard 80 gallon, 24 MBH heater. (5 people, 3 baths) All zone valves are in parallel, and there is a taco 007 pump on the return pushing into the boiler. The water feed is on the suction of the pump, but the expansion tank is on the discharge of the pump, on the boiler top tapping. The system pressure was at 25 lbs (30 lb blowoff), but the owner said that the blowoff didn't drip (yet- I told him).( see the attached sketch)
OK, I told him that i could fix this. The most obvious problem was the lack of flow to the indirect water heater. The 007 wasnt cutting it, so I told him that he needed a pump dedicated to the DHW. I went to the Bradford white website to gather information about the water heater. I reviewed all technical information and NOWHERE did they have boiler water flow and pressure drop information. How does one size a pump to supply enough boiler water to meet their published specifications? This is essentially a shell & tube exchanger (boiler water in the tube) so there will definately be a significant pressure drop. I will have to call tech support to get this information, but I would not be surprized if they didn't know what I was talking about.

Any way, until I get better information, I decided to use 100 & 50 feet of 3/4" copper pipe as my worst and best case system, and plotted the curve on a Taco IFC pump selection chart. (see attached)At this point I would select the 008. What do you folks think about it?

The next problem is the pump on the return. I have read Dan's Pumping Away book, and always design as per that. At least the water feed is at the pump suction, but the expansion tank isnt. That is easy to move. My problem is that with the additional parallel pump installed, the "point of equal pressure" is on 1 pump suction, and not the other. WILL THIS BE OK?
I am not trying to create a bigger job for myself, but I am thinking that I have to make this system "right". I need to move the pumps and the point of equal pressure to the boiler supply side.
Comments?
thanks

ALH_4

Indirect

Ideally the expansion tank would be tee'd in at the suction side of the pump. What model Bradford White water heater is it? I have run into that same problem with finding pressure drop information in their literature. A few years ago they had the head loss curve on their website, but from what I can no longer find that sheet. Certain models of their water heaters have a coil with a VERY high head loss. It takes a large pump to move enough boiler fluid through the coil. When I have contacted Bradford White, they have been helpful.

Zoning an indirect water heater with a zone valve already provides a somewhat less than ideal situation for rapid DHW recovery, because the valve created additional pressure drop, and the boiler pump may not be able to provide the required flow rate for the water heater. Add that to the head loss of the water heater coil and you have pretty slow recovery.

Hopefully the LWCO is above the boiler.

What to do now? I recommend upgrading the system using a reset control with DHW priority, piping the system per the diagram under heating "Section C-2" on page 9 of the Tekmar 260 data brochure. If the water heater is the (edit) Powercor with the long small diameter coil, I would use a Grundfos 26-99 as the DHW pump.

hr

the 40 gallon won't perform like the 80 gallon

when you are looking at dump loads.

Is the tank a new Bradford White PowerStor I believe is the name? If so it has a 1-1/2" coil and pressure drop should be nil. Sounds like the 3/4" pipeing would be the bottle neck? It would be nice to move 12 gpm or so through that coil from the boiler, as the boiler on priority could provide the hp. Not easily done with 3/4 copper, however.

The older version Bradford White tanks had a 5/8" coil. Quite a bit higher pressure drop. I doubt it would handle a 150K input happily

The Bradford White website should help you determine which version you have, all the data as well as performance is available there. Be sure to look at the btu input numbers, and boiler temperatures they use to rate performance.

hot rod

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hr

The P-40 R10

is the style with the small diameter coil. The installation manual, available at the website, indicates a max 5 gpm through the coil. Guess what...

hot rod

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tim smith

Priority!

I would think that the 007 would do the job as long as the zone valves were on priority for dhw. Put a priority zone relay in so heat zones lock off when dhw calls. JMHO, Tim

steve b_29

Just a homeowner who wants to understand the way his own indirect heater operates...

I understand that it is important to have enough pump capacity to the indirect. But if there still isn't enough hot water, couldn't the indirect's output be improved further by operating it at a higher temperature and mixing down to 120 deg. or so with a thermostatic valve?

Would there be anything to be gained by the indirect's aquastat having a larger differential when the indirect operates at a higher setpoint?

ALH_4

Output

Yes, you can run the water heater at a higher temperature to provide more hot water reserve. Of course you are always limited by the boiler's output.

I mention the indirect heat exchanger coil in this case, because Bradford White did make a water heater with a coil that had incredibly high head loss (something like 60 feet at 5 gpm), and it can easily be possible that no widely used hydronic heating circulator will deliver the boiler's output to the water heater.

I dont think a particularly wide differential on the water heater would have much benefit, but I could be wrong depending on the circumstances.

hr

more output

is possible with higher tank temperatures. Be sure to check the max temperature the tank manufacturer allows. Some are limited to 160, or less.

Also be sure you use the correct, LISTED tempering valve of the correct capacity.

Higher tank temperatures seem to cause more mineral and sediment issues, from my experience.

Ideally you would determine your DHW needs and size the equipment, tank, circulator, and pipe size to that load and spec.

If you feel you are close to the "goal" a bit higher temperature may help.

Or a solar DHW pre-heat system

hot rod

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Rich Kontny_5

Hot Rod

What if any problems do you see with a well insulated Triangle indirect water heater (82 gallon) piped as the primary loop (controlled by domestic heater aquastat) set at 145 with the indirect return side having the secondary space heating zones taken off before it returns to the boiler.

We used a 1" Sparco tempering valve to bring down the domestic water to 125. We used smaller Sparco tempering valves to set temps for in-floor and other space heating design temps.

The indirect gets priority while acting as a buffer tank. It has been five years and this system has neer been short of hot water or had cold floors.We however used a power vent SlantFin cast iron boiler that has about 80-82% efficiency.This was a million dollar new house with 4 1/2 baths.

Would I be able to do the same thing with a mod-con that is more efficient?

hr

I have a few Ultras installed like that, Rich

and a Munchkin. They work very well. Just as long as the DHW load isn't too large, and or long, to prevent space heating
Most mod cons have a time out adjustment to prevent endless DHW priority calls.

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Rich Kontny_5

Thanks

Thanks Hot Rod I could use a seminar on Mod-Cons. Maybe Dan and you could get your heads together and set up some.

Rich

laurence salvatore_2

indirect

I was taught to pipe the boiler supply and return at least one pipe size larger than the tappings on the indirect up to 2" (some phase IV's). A zone valve is less than ideal but should work as long as it is follows the one pipe size increase rule. I have mine own superstore 40 gal. piped with a 1" honeywell zone valve on 1" copper and my family of 5 has a hard time running it down with the aquastat set around 120.

Joe Mattiello

Hi Bill
After reading your thread, and the Wallis’s correspondence, collaboratively you have compiled enough information to correct the domestic water woes. You mention a zonevalve, and ¾” piping approx. 150 lineal feet. I’m not sure of the valve mfg, but taco 3/4 “ zonevalve has a 6.1cv, which creates 1.55 ft head pressure drop with a 5 gpm flow rate, and the 5 gpm through 150 lineal ft 3’4” piping has 9.48 pressure drop. Collectively, that’s 11 ft hd, without considering the pressure drop through the boiler, and indirect water heater. I wouldn’t select a pump until you have all the information required to size a circulator. However, you can:
• Change the pump location to pump away from the point of no pressure change.
• Omit the zonevalve, and use a pump with an integral flow check
• Increasing the line size from ¾” to 1”
Hopefully, this helps

hr

Here is the pressure drop chart for that tank

If in fact it is a PowerCor.. As you can see 5 gpm is a whopping 53 ft of head. I'd say 4 gpm is more realistic although still 35 ft of head. The HX is 80 feet of .55 id tube, a fairly constipated HX.

So based on this the heat exchange in that tank at a 4 gpm flow may not get 'er done to your liking

hot rod

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bill nichols

reality bites

thanks hot rod, and all the other folks for your help.
First thing this morning I got the pressure drop info from Bradford white, a response from the email that i sent them. and yes, to get their published output, i need a pump, 5 gpm @ 58' of head (25 psi) (yea- right).
The best that I can do off the Taco IFC selection chart is the 013IFC to give me 3.8 gpm@ 29', or the 009 about the same gpm @26 ft. Can I do better with another pump? (nobody commented on my pump selection)
I am not looking for ideal here, its not my design or installation, I just want to maximize the equipment thats there already and get the family some hot water for their morning showers.
To make the system "right" the suction side of the pumps needs to be common where the water feed and expansion tank is. to do that, I have to move the pumps to the boiler discharge. Right now, the way that its piped I can only common the discharge of the pumps, and this messes with the point of equal pressure. Its not a big deal to move the pumps, just a few feet of pipe and some fittings. I have to get this done in a day, and I work by myself. I can probably stage the parts and do some pre assembly, then shut down and do the installation the next day.
thanks again for all your help.

hot_rod

an odd duck, a circ like that

I wonder that two circs in series may be another way to get high head, ultra low gpm? Good question for a pump expert.

You may end up with some sort of primary secondary pipe arrangement or a hydro separator to keep that much circ away from the rest of your system. Hydraulicly speaking.

Or switch to a tank with a lower pressure drop, and maybe even more gallon capacity to assure the performance they are expecting.

hot rod

Jason Quinn

Pumps in Series and Parallel

To expand upon Hot Rod's suggestion, according to Grundfos' "pump basics" information in their technical info, to achieve higher heads, operate two or more pumps in series and to achieve higher flows, operate two or more pumps in parallel. I hope this helps?

Rich Kontny_5

Heat Exchangers

Hot Rod,

Since all heat exchangers are not created equal, I wonder what kind of pressure loss occurs across flat plate heat exchangers. The packaged pump(s)in the "Heating Box" I use to heat my kitchen infloor seem noisy in comparison to regular cartridge type pumps.

I suspect they are sized to overcome the HX pressure loss plus an average sized hydronic system. I would like to put a buffer tank in and see if the Takagi I use for a heat source would keep up with both the domestic load and my space heating needs.

There really needs to be a think tank set up to consider options relative to loads. With as much product out there for both heat sources and distribution systems it is getting confusing for not only homeowners but old school hydronic installer's (that would be me)

With the new energy saving pumps on the market the rules are changing faster than we can keep up.I see the days of combined plumbing and hydronic contractors splitting to specialists who concentrate on one or the other.

As with pipng systems you almost have to pick an innovative and cost effective system and stay with it. We have pretty much done that with "Uponor" it makes inventory,design and training simpler.

Problem is our heating dept. is scorched air first with hydronics second. They are slowly getting into "Munchkin" installs but we rely on one wholesaler for both HVAC and hydronics. This means we are limited to the lines they stock.Recently they hired a very competant hydronics designer, however he runs into the same reluctance from the wholesaler to take on new and improved lines.

Venting a little bit here but trust me we discuss this very often!

hot_rod

Rich

the pressure drop in a heat exchanger relates to the amount of gpm you are trying to shove thru 'er. The maker of the HX has software available to know that. I suspect the pressure drop thru the tankless has a lot to do with that pump size?

Knowing the numbers you could plot the operating point on the pump curve. A noisy pump is often an air issue, or it is running way off curve. Or both

I agree hydronics has become a lot like refrigeration.. a fairly specialized field. More and more it is running outside the comfort curve of many plumbers and pipefitters.

The good news is there are pleny of classes, online and other, to get any willing mechanic up to speed. It is just a matter of willingness and time.

hot rod