Wish I had a testing lab to try this. (PR)

Paul Rohrs_2

Mark,

I know you are busy, any updates on the variable speed flow that you could tell me about?

Regards,

PR

Paul Rohrs

Thinking about setting this up as a test

Let me first say that I am only batting this idea around. I stock and sell Rinnai tankless heaters. The commercial (external mount) unit can be programmed from 96°F - 180°F water temp. Again, the Rinnai only fires upon demand based on flow through the unit. No Flow, no fire. Also, this is a modulating burner that fires proportionally based on the water inlet temp and outlet temp. It comes with a control to set the desired water temp. Let's say for the sake of argument that this unit can put out 6GPM of 180°F water non-stop. Wouldn't that be enough to satisfy quite a few heat demands?

Why not use this in conjunction with VSI system and cutout the primary loop?

What you are looking at is the injection loop and the secondary system loop. (See Rinnai Mechanical.JPEG)

I used a promix 201 from Wirsbo in this drawing. (I am not an artist, but I play one on TV) Of course, you can use your injection control of choice. Go Tekmar!

This is set up as a constant flow since I have taken 24V to the Mix Demand. This will drive P-2 until WWSD, P-1 will ramp up and down and regulate the burner modulation in the Rinnai. (See Rinnai Electrical.JPEG)

I wanted to put this out on The Wall to see the different input I might be missing. (Yes, I know that Rinnai has a minimum operating pressure of 40PSI.)

I welcome all responses, positive and negative, but please leave my Mother out of this. (Heh!)

Regards,

PR

Mark Eatherton1

Yo mama...

raised a pretty smart boy:-)

Are Rinnai' a fully sealed combustion process, or is modulation done by lowering the flame but not the secondary excess air? I fit's the latter, thier thermal efficieency suck a lot of cooling air through their fire box when on low flame. If it's a sealed combustion unit reminiscent of the Munchkin, it might work. I'm going to be doing some experiments with my lab regarding variable speed flow and variable flame heights. I've done variable speed on my one pipe main before, and it worked pretty cool.

Anyway, what you're proposing would work. It's just a question of lower end efficiency.

ME

Steve Eayrs

Paul, Last year I installed (3) Rinnia Continuummmm commercial units, (the ones you are talking about), as radaint floor heating units. Two of these were done injection pump, (tekmar), with a bigger pump (26-99)pulling directly off the units, then injecting into the secondary loop. Had problems with the burn cycles. Way too short. These unis are designed for cold in and hot out. Didn't seem to matter where I adjusted the temp. on the unit. Ended up burning up way too much fuel. Big enough difference, that I have removed one and installed a boiler, at the owners request, and believe I will end up doing the same to the other one this year. Of course at cost or less, due to my desire to experiment.
The third unit I installed p/s, (to keep the proper flow through the unit), and simply installed one of the Rinnai wall controls to adjust the aprox. water temp. I want in the floor. No I/O or injection controls. Set the supply temp. to 130 deg., and instructed the owner how to turn it up or down if required.
The first two units were in concrete or gypcrete slabs, but this third one is a staple up. He has turned the temp. up to about 140 deg. this time of year. They say they like it.
I personally will not do any more system like this, since even this one does not cycle like I would like and I know the $$$ spent on fuel are higher than a good boiler would operate at, due to the cycling. (maybe even as much as 50% higher?) Hard to say, since all three of these places are quite different from each other, in size, etc..

Also had some problems with vibration noises in the unit. This was the clincher on the one we removed, to the owner.
In my opinion the install was not a big enough savings to warrant the higher operating costs, on the systems we did the tekmar and all on, to warrant not going with a boiler.

As far as the 40# min. pressure I believe that is only refering to an open system like a domestic hot water system, where the pressure is directly related to the rate of flow. I don't believe it is at all refering to a closed system like a boiler system, where the flow rate is directly related to the pump and piping size.
(on a closed system the flow will not move any fast if you increase the pressure from 15# to 40#. In fact their will be no flow at all, unless you turn on the pump.)

I'm sure I am not telling you anything you don't already know, but keep in mind the high pressure drop through the Rinnai, and the need for bigger pumps than normal.

If you try this please let me know how it works for you. I may have missed something on the design of mine.


In hind......sight I would only install one unit and wait a year os so to see how it works, but you know how it is when the ball is rolling and people want it done now.


A number of few years ago I install a similar type unit (Myson), and pulled directly off the unit with the injection pump, but it was for a low btu building, not a whole house. It still is working fine, as far as I know. (come to think of it, its been years since I have heard from the owners of it).

Steve


p.s. Just looked at your drawings, which I should have done before I rambled on forever.
I don't think you will get the flow high enough through these units, to ramp up the burner, when the injection pump is running at anything but about full speed......but would be interested to know how it works for you.

Paul Rohrs

More info

These units are not considered sealed combustion,(but they should). They physically mount on the exterior of a house. They draw combustion air from outside and exhaust it outside. They have multiple thermister type sensor that safeguard it against freeze up. (Down to -30°F)

These units are 190,000BTU input at roughly 82% efficiency. They have 10ea 19,000BTU burners that modulate. They have a variable speed fan that controls the rate of combustion, much like a MunchkinPinnacle.
This thing low fires at 19,000 BTU's. They max out at 8.2GPM .

40PSI is a minimum standard. It has a 58 copper heat-exchanger that needs higher pressure to overcome the head loss. (pretty high head loss) I think Hot Rod called it an invitation to cavitation.(Great quote)

I have used this unit on a small radiant slab-on-grade job. Used a higher head pump and dialed in the temp to send straight to the floor. Works fine. It sounds a lot like Steves system but my system flow rate requirements were low enough to handle the load. Steve, I think a buffer tank would have helped with the volume and flow issues off of a primarysecondary loop.

This particulary interests me because the Rinnai is only based on flow through the heat exchanger. (These are designed for DHW) Just thought the injection idea would be worth trying especially since I dont have to worry about return water temps.

Dial the temp for injection at 180°F, return from my secondary system at 100° to 105°, burners modulate to my Delta T, probably on high fire at design conditions.

My gut agrees with ME in that on mild days, the variable speed pump flow rate might be 1-2GPM, but the burners will be firing at 50% or 95,00BTU's to meet the demand.

The application would be great for Siggys mini-tube systems but without the rest of the mechanical room. Wouldn't it be an easy installation to locate these around a large facility in remote areas? Truly a remote mini tube system. The downside is the redundancy of air-separators and expansion tanks and other necessary items. You would have to really crunch the numbers to see if it makes economic sense on different sized jobs.

Just thinking some more.

Regards,

PR

kevin_5

Run for your lives!

I personally know this Paul character, and he could be dangerous. Two words for you guys- Doctor Frankenstein
;-) Kevin (Don't take me jokin', I'm only serious.)

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hr

The first ones

wouldn't modulate right when they started seeing warm return temperatures. The factory guy told me they were tweaking the program to deal with this for heating applications. That's been a year or more ago when they came to this market.

I looked at some for radiant, the double walled OEM venting and fittings are VERY expensive, if you want to bring them in from the cold No substitutes.

And the pressure drop through the HX is real high. The output is 6 or 8 gpm max, as I recall. Limits you to a 60K load at 20 degree delta T. Why buy 2000,000 input for a mere useable 60 k out?

All in all I think they are best left for instantanous DHW jobs. Especially with all the excellent modulatiog, code approved units currently on the market for hydronic applications. The small Ranni price tag makes them look attractive, too much baggage comes with a sucessful hydronic marriage, in my opinion

hot rod

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Paul Rohrs

So I cant achieve an 80° Delta T?

That was going to be the only saving grace with this setup.

If I can set this up for 50° inlet and 130° output for DHW, the same math won't apply for 100° inlet and 180° out?

I might call tech assist and ask. I know they get a little skiddish on closed loop heating systems with the residential unit. You must use the commercial unit or they void the warranty.

I agree with HotRod, the venting material is pricey. (Gross National Product of small countries.) I am partial to the outdoor unit anyway.

Thanks for the responses.

Mark Eatherton1

I can tell you this...

the T-50 is MUCH too smart to be fooled with variable flow. I've not had a chance to try it with any others Paul. Up to my butt in alligators, and still looking for the drain to the swamp.

ME

Steve Eayrs

Hi Paul,

I only used the indoor commercial units on my applications, due to too cold of winters.


Not one of the loads exceeded 50mbtu on the problem systems, unless the indirect for dhw kicked in, and demanded more.


My original thought were the injection would work fine, but I came to the conclusion that I really wasn't saving anything after trying to turn them into a boiler. Fuel cost were defintely a lot higher than a good boiler. Concluded this was mainly due to inefficient cycling. Its hard to maintain a big delta T if you don't have a big demand. If you do have a big delta T you most likely also end up with uneven heated floors, since the first 1/2 of the loop has to be a lot hotter than the return. right?
Of course if you add enough stuff buffer tank, mixing, etc. you may make it work.

Yes a buffering tank may have helped, but kind of defeated the objective of coming up with a cheaper system. I also have a problem with adding a buffering tank to a heat system. Kind of the weakest link, and shuts the whole system down if it springs a leak. (chances are it will go first, before the boiler or anything else)

Have installed plenty of these for their intended purpose....water heaters, but concluded I don't like them at all as converted boilers.


One last comment. Look close at the Rinnai recommended drawings. Some are impossible. Would never work. I know they state they are not intended to be used for design purposes, but they are not ever a bad design.

They actually show a couple drawings with a pump pushing directly through a pressure reducing valve, with a check valve on the return. This is all tee'd off for the house heat side of things, and the house pressure is running through the unit. Evidently they think you can have two different pressures in the same boiler system, without using a heat exchanger. Like to see the size of the pump needed on the low pressure side, to push the return through the check valve, to the high pressure side.
Told them about it and they stood behind their drawing, and said it would work. Definitely not boiler people.

Steve