Source strangulation for an instant water heater?

[Asymptotic]

You are misapplying the manual: the 37 degrees-3 LPM pair assumes a standard input temperature that is not available here so it is a pointless thing to say or test for.

Outlet temperature (37°C), flow rate (3.0 LPM), and power (6KW) are given. Inlet temperature can be calculated, and works out to approximately 8°C.

8°C (48.4°F) seems a reasonable value. Several years ago at the plant I measured city water temperature at the mains meter from early January to early August to get a sense of seasonal variation, and found it ranged from about 40°F during a cold snap to 70°F during a heat wave.

 

[Asymptotic]

How about this for a reason: you do not grasp that the 37 degrees is up to the taste of the user

37°C is from the specification table.

So taking measurements without a mathematical foundation to use them would be akin to playing.

This is an unusual perspective. Would Johannes Kepler have developed the math underlying the laws of planetary motion without his and Tycho Brahe's observational data?

 

[sysprog]

Outlet temperature (37°C), flow rate (3.0 LPM), and power (6KW) are given. Inlet temperature can be calculated, and works out to approximately 8°C.

8°C (48.4°F) seems a reasonable value. Several years ago at the plant I measured city water temperature at the mains meter from early January to early August to get a sense of seasonal variation, and found it ranged from about 40°F during a cold snap to 70°F during a heat wave.

In Chicago, the source is Lake Michigan, far enough out and deep enough down that even by the time it gets to residential areas 10 miles away from the filtration plant, even during a heat wave, it's still pretty cold, around 50-60°F.

 

[sysprog]

37°C is from the specification table.
View attachment 247567

So taking measurements without a mathematical foundation to use them would be akin to playing.

This is an unusual perspective. Would Johannes Kepler have developed the math underlying the laws of planetary motion without his and Tycho Brahe's observational data?

Yeah, and what if Galileo had said he wouldn't look in a telescope until Newton came along with a mathematically justified prediction of where each planet would be when (inconvenient, given that Newton was born slightly earlier in the same year as that in which Galileo met his demise), oh and yeah, Newton made some 'preliminary observations' too.

n.b. @Jonathan212 said he had the DH106101 (one column to the left of the one indicated by your arrow), the specs for which are exactly the same, except that the fittings connection is 1/8" on the DH106101, and 1/2" on the 111, and no, to anyone who might suppose otherwise, that doesn't make a whit of difference, except possibly to robustness, and the 111 has a green 'on' lamp, which also has zero effect on performance.

 

[Asymptotic]

n.b. @Jonathan212 said he had the DH106101 (one column to the left of the one indicated by your arrow), the specs for which are exactly the same, except that the fittings connection is 1/8" on the DH106101, and 1/2" on the 111

You're right. My bad :)

 

[Jonathan212]

The math is 100% known for this problem. Nothing to do with Kepler's situation.

But it is not known to any of us here. Yet. We're still missing the copper equation as opposed to hose, the circular turn equation, not sure about the elbow if it is copper rather than what? Once we have everything down, then is the time for measurements, we will then know which set of measurements is sufficient and which is not. And hopefully skip the gauge purchase. Then I would predict what a thicker pipe would do or size a pump.

 

[sysprog]

The math is 100% known for this problem . . . But it is not known to any of us here.

That remark strikes me as extraordinarily presumptuous.

 

[jrmichler]

I just read through this thread. Except for a couple of digressions, the discussion fully covers what is going on with the water heater. The discussion also covers solutions.

While I see no need to calculate pressure drops, it would not hurt to do so. Calculating pressure drops is a good way to better understand the water system. For finding pressure drops in piping systems, the best resource is Cameron Hydraulic Data. The latest edition is quite expensive, but the earlier editions are just as good for water flow through iron and copper pipes. In the U.S., it is readily available by interlibrary loan if one does not want to buy it.

 

[Asymptotic]

I just read through this thread. Except for a couple of digressions, the discussion fully covers what is going on with the water heater. The discussion also covers solutions.

While I see no need to calculate pressure drops, it would not hurt to do so. Calculating pressure drops is a good way to better understand the water system. For finding pressure drops in piping systems, the best resource is Cameron Hydraulic Data. The latest edition is quite expensive, but the earlier editions are just as good for water flow through iron and copper pipes. In the U.S., it is readily available by interlibrary loan if one does not want to buy it.

Several editions of Cameron Hydraulic Data are available to borrow at archive.org, and older editions can be very reasonable to purchase. For example, Abebooks lists 30 volumes ranging from $9.95 to $52.
https://archive.org/search.php?query=Cameron Hydraulic

The Copper Tube Handbook is also a valuable resource.
https://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf

 

[Jonathan212]

Surprise. Three different kinds of copper K, L, M with pressure drops of the order of 45% higher in K compared to M. Looks like the type of copper will have to be discovered too.

 

[Jonathan212]

Recommendation to sysprog (system programmer?). Do not take this forum so seriously.

 

[sysprog]

Recommendation to sysprog (system programmer?). Do not take this forum so seriously.

I think that you should not presume to make such a recommendation to another member.

 

[Jonathan212]

You are only projecting.

 

[sysprog]

You are only projecting.

This sort of thing belongs in private messaging if at all. Please don't continue to pollute your own thread with it.

 

[Jonathan212]

If a new pipe is installed, it will be of the following type. Do we have the data for multilayer pipes like this?

 

[OmCheeto]

... Three different kinds of copper K, L, M with pressure drops of the order of 45% higher in K compared to M. Looks like the type of copper will have to be discovered too.

According to wiki, the three types of copper pipe have the same exterior diameter, but due to their varying thicknesses, they have different inner diameters, which accounts for the different pressure drops for pipes of the same exterior size. [ref: wiki]

I'm certainly learning a lot more about piping than I had intended.

ps. For future reference, Jonathan212's assertion is correct, and is based on the chart and equation on page 79 of the Copper Tube Handbook pdf mentioned earlier in post #69.

Table 14.6 is based on the Hazen-Williams formula​

P = 4.52*(Q^1.85)/(C^1.85 * d^4.87)​

Where:​

P = friction loss, psi per linear foot​

Q = flow, g.p.m.​

d = average I.D., in inches​

C = constant, 150​

and per wiki:

size	OD	ID
		K	L	M
1/2	5/8	0.528​	0.545​	0.569​
3/4	7/8	0.745​	0.785​	0.811​

 

[bhusebye]

Think of Pressure this way. You have the self car wash down the street, how big is the hose? More pressure smaller hose, BUT it will not make enough of a difference to go from 3/4 to half. Bigger pipe means more volume for the house and means water will reach farther and supply more fixtures bathrooms, kitchens and so on sufficiently. And those that do not believe me, I used to be a plumber :P

 

[JBA]

That is the exact reverse of the reality that the smaller hose, which can be rated for a desired higher pressure supply and flow and still be flexible, is the result of the higher pressure requirement, not the converse.

 

[NTL2009]

Sorry I'm late to this, I had read it on my tablet and it was too hard to respond there. I may have missed it somewhere, but I really think the solution is far simpler than where these posts have headed.

I really think that trying to work to increase pressure/flow at the input is barking up the wrong tree. From the OP: "probably as it senses low inlet pressure." - The heater sense flow, not pressure. There was a chart in post #62 that showed the turn on/turn off points to be at 2.3 and 1.8 L/min. So once you are drawing hot water, you need to keep the flow above 1.8L/min, or the heater will shut back off. As the OP mentioned the problem is worse in warm weather, this makes sense, the user adjusts the faucet for a hot shower, but that takes less draw from the hot side in the mix, since the cold side is warmer in warm weather. This was touched on in post #5, but seems to have gotten lost.

The simple solution is to run a separate hot water faucet as you shower, to bring the total flow of hot water higher than 1.8L/min. Somewhat wasteful yes, but that's the simple solution.

My shower is ~ 4L/min total flow. OP should measure theirs. This was asked in post #37, but was rebuffed by OP. I guess maybe they don't want help?

I think another, more complex and costly solution was mentioned, to add a small-ish tank heater at the output, to buffer the on-demand heater. But that will also go cold eventually w/o enough flow to trigger the demand heater on.

 

[bhusebye]

You could put a insulated loop in with a Grudfos pump. That might work.

 

[Heri]

Keep it simple... Chances are, the shower head is where flow is restricted. Just use a shower head that allows more flow. You may test it by removing the shower head from the hose and try if the heater shuts down or not. If not, the shower head is the culprit.