Specifying ECM circ pump for 23 unit apt building with unusual heating system

Eli

The building is from 1963 and is zoned by apartment (24 zones including office). Radiation is by radiant panel. The "baseboard" is 8" tall and 3/4" thick; behind it is a simple 1/2 copper loop. Amazingly, it works amazing! The boiler room has twinned gas fired boilers and the system pump is a B&G HD3. Christmas morning, the pump stopped and we got it going with a screwdriver and some oil but I take the warning to heart and am shopping for a high-efficiency replacement pump.

Using Dan's sizing method, I am looking for 45 GPM (2" piping at the pump) and 22 Ft. of head, based on 130' to the most distant apartment plus another 50' of baseboard in that unit. (180' x 2 x 6ft head/100 ft).

So far so good. Except the dying B&G is nowhere near that output. At 45 GPM, the B&G is rated for 16' of head.

So what do you think? Should I match the B&G spec or size it for the math? Again- it's been working well for the 10 years we've owned and managed the building.

I like the Grundfos Magna3 40-80 which, at 45 GPM is just a hair under 20 ft. It gives some more oomph compared to the old B&G. Is the auto-adapt the right way to go with an old, unknown system like this? I like it over the Taco VR15-1 which appears to have a set up WAY beyond my pay grade (I'm an M.E., but not a heating professional).

Thanks for any help and happy 2017 to all!

EBEBRATT-Ed

The easy way out is to match the old B & G spec, "if it aint broke don't fix it".

That's what I would do.

If your picky, install good quality pressure gages at the pump inlet and outlet. Convert the gage readings to ft of head. Subtract the suction reading from the discharge reading. Get a pump curve for the old B&G and see what your pumping now that you know the actual feet of head.

or

Install a "circuit setter" balancing valve in the pump discharge pipe and hire a balancer with the correct readout probe to measure the flow

You may have 2" pipe that doesn't mean your flowing at 40 gpm. 1 1/2" is good for somewhere around 25 gpm so lets say your system was designed for say 32 gpm it would still need 2"

Look at the btu OUTPUT of both boilers and add them together and devide by 10,000 (for a standard 20 deg. TD) see what gpm you come up with. It will probably match what the old pump was sized for.

I am assuming both boilers need to run to heat the building with no redundancy

Eli

Thanks Ed and Hatteras-
That was just the reinforcement I needed to move forward. I wasn't aware of the 'divide by 10,000 to get GPM'; that's a helpful rule of thumb. We replaced the original single-pane, aluminum windows a couple summers ago and updated our schedule J to arrive at est. 235 kBTU; so approx 24 GPM. Without the windows, the 2" pipe would have been the right choice (as it is, 1-1/2 would probably be fine when we repipe the boiler room). At that rate, the current pump can deliver 18 ft. of head. At 45 GPM for a 2" pipe, the old pump can deliver 15 ft. of head. So that has the pressure bracketed from 15 to 18 and I'll fudge and say less than 30 GPM. That puts me very comfortably under the curve for the Magna3 40-80.
Unless you hear back from me, it worked out great!
Actually, I'll update in a while with electric savings; at est. 500 watts, our current pump is costing about $260 per year in electric.
By the way; as an apartment operator, you pros can help us justify upgrades with this rule of thumb: multiply any annual savings by 15 (17 in a high-worth area) and that's the increased value of the building. Example: I expect the ECM pump to save $180 per year in electric costs- in our area that will make the building worth $3,000 more (17 is the the inverse of a 6% cap rate [http://www.propertymetrics.com/blog/2013/06/03/cap-rate/]). Not bad for a couple hours work. If you have multi-family operators as customers please go out and sell them on any upgrades with residual savings. I can get a 3 month !!! payback on low flow toilets. Email me directly if you need help selling this kind of work. There's not a building in your neighborhood that doesn't need new toilets (Niagara Conservation .8 gallon flush). I love conserving resources; esp. as it's a win-win (as compared to rent increases, uncharges, etc.).

Paul48

The current circulator will not pump 22 ft/hd, so that calculation is wrong. You're looking at the pump curve backwards. You can't select a flow to generate ft/hd. The system has so many ft/hd that exist in the piping. With a fixed-speed pump that determines the limitations of the pump (circulator).

Eli

Paul 48, I think I understand what you are saying. I am trying to infer the system's frictional losses based on the existing pump. So since the pump can produce a pressure of 15 to 18 ft within the possible flow range of a 2" pipe (0 to 45 GPM), I'm inferring that my system loss is in that range. Would you agree with that logic? Ultimately, I'm going to depend on the temp and pressure sensors in the Magna3 to make the call, so long as the system requirements are within the capacity of the Magna3 40-80 (which I feel they are based on the comments herein and the existing pump).

Eli

OT- @ Hatterasguy:
Agreed, off topic, but I happen to love this business and can't resist a lob. The cap rate is a good, if blunt, tool to compare investment opportunities. The way an investor makes money (without too much of a deep dive here) is with leverage and appreciation.
Example: I have $100k to invest. I buy a $400k triplex at 6 cap with a 75% loan. Right now, we can get a commercial loan in the low 4's but let's use your example of 5%. So on my $100k, i'm making $6,000 and I'm arbitraging the rate on the $300k loan, so I'm making 1% of that, $3,000. (Not considering for a moment the principal payment which flows to my equity anyway). In my region (Phila) rents are moving at north of 4-1/2% per year. But let's assume the building appreciates 2% per year just based on market forces (this is conservative). That means the $400k building is worth $408k at the end of year one.
So in year one I profited $6,000 (on my 'down money') plus $3000 on the difference between the loan and the return, plus $8,000 on appreciation. That's a 17% return on my cash investment.
There are other benefits- most notably is the ability to depreciate the asset over 27.5 years (which will drive up the expense number lowering the tax burden, which will be recaptured at sale, but it's still a nice loan from the gov't- like it or not from a policy standpoint).
For me, the real fun is finding opportunities to improve an asset once owned; such as upgrading to ECM pumps, LED lights, insulation, nicer kitchens and baths, providing exceptional service to the tenants so that I lower turnover costs and eliminate vacancy losses. Once word spreads of our service, we build a wait-list for our apartments, etc.

I'm eholtman@narberthapartments.com if anyone is really interested in some investment tips. Always happy to pay it forward. I happen to believe that if you can wear any type of tool belt, you should own at least a little investment property. Knees don't last forever.
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Paul48

The only thing that can be inferred, is that your system head loss is under the 19+ ft/hd that the B&G circ is/was capable of pumping. With the range the Magna3 has, you should be fine. I tend to get stuck on "knowing" things. Maybe it's obsessive, I don't know. I just hate not having answers. Here's a scenario.......The new circ is not performing well. Someone says,"How many gallons per minute were you pumping with the old circ, that worked well?"

Eli

That's a good point Paul. As a recovering engineer, I'm also a big fan of data. I imagine the magna will report the system head and I can consult the curve for the old pump to determine what the actual flow was.

hot_rod

The Magna 3 is a pretty clever pump. The large data screen allows you to set up and watch performance as text or a graph. here is some of the tricks it can do.

We use one in our test lab to dial in specific tests, the readout for pressure and gpm is very accurate.


https://www.youtube.com/watch?v=kg7DIv8AL3w

Eli

Update on the Grundfos Magna 40-80:
Well, I installed the pump on January 12th and it's logged over 400 hours. Here are the results: the peak load on the pump so far has been 45 GPM at 14 feet of head. Damn if that isn't right on the curve of the old pump. I couldn't be more impressed with the dead guy that figured that out!

With respect to Dan's calculator, this system is using every bit of 2" pipe capacity; however the head loss estimate was over 50% too high. Maybe because it's an all-copper system?

I actually had the good fortune to meet the developer of this building a few years before he passed. I wish he was still around to hear this story. The additional good news is that if I'd known this info before installing the 40-80, it's still the right pump for this application. I haven't been through billing cycle yet, but will update with electric savings and be able to accurately share the payback period on the pump. I have to say, the Magna is a slick piece of kit. I had to add a relay to provide a dry contact for the pump (it needs 120 v all the time but uses a dry contact to shut off during DHW priority) but otherwise was a pretty easy swap over.

nicholas bonham-carter

Very interesting comments on the cost benefit of such a pump. At least you know that the pump will pay for itself in a few years.
What are you flushing those toilets with for such a quick payback-Perrier water?--NBC

EBEBRATT-Ed

If a system is properly piped the actual head required is usually less that the calculated head.

Glad it matched up well. The original designer knew what he was doing.