DIN / NPT compatibility?

[Ginahoy]

I'm specifying an imported chiller for a project. According spec sheet, water connections are DN25 1"

I checked with the distributor and he claims DN25 is the same as 1" NPT.

At first I thought DN25 meant DIN25, which I don't believe is compatible with NPT. But I now realize DN is different than DIN...

DN = "diametre nominel" (ISO)
DIN = "Deutsch Industrial Norme"

Too confusing!!

But just be to safe, can someone confirm that my plumber can connect to DN25 with 1" NPT fittings?

 

[BillTheEngineer]

I am going to speculate that they are not the same. The pipe size may be similar or the same, but pressure rating and material properties probably do not match up either. I am also going to speculate that the threaded connections are not compatible with the NPT thread form, I would guess that they are either BSTP or BSPP (British pipe threads, tapered and parallel). A npt thread will engage a thread or two, but won't seal properly.

The easiest way to check is get a thread gage and see what it is. or get fittings and see what fits. The BSPP seals with a face seal gasket or o-ring. The BSTP requires a thread sealant.

 

[Sponsor]

 

[DougB]

"I'm specifying an imported chiller for a project."

I feel sorry for the customer. Wait until he needs parts.

 

[Ginahoy]

@DougB, I'm normally the guy advocating for tried-and-true mainstream products. Too much risk at the bleeding edge, or niche products. Here today, gone tomorrow. But in this case, because this is an off-grid home in a hot climate (e.g, near Phoenix), the cost of not going with this product was significantly higher than the risks. The problem is that no US company makes a small (less than 3-ton) reverse-cycle chiller with an inverter drive compressor (e.g., negligible start-up current). By using a chiller as opposed to an air-to-air heat pump, we can stored cold water to get through extended periods of low insolation, in lieu of having a room full of batteries. The design objective was to keep the house cool for 3 days without sunlight or generator ops. That requires a LOT of storage capacity.

The importer is a mature company that specializes in solar power systems (mostly government contracts). They designed this chiller, which is made in China, specifically for off-grid applications. They specified readily available off-the-shelf components (compressor, heat exchanger, pump, fan motor, valves, etc.) to keep cost low. The biggest risk is the control board, which is custom. We can purchase a spare board or perhaps even a spare chiller ($3.4k), to reduce risk.

My design saved the owner more than $50k on power systems cost (PV, batteries, inverters & charge controls) compared to what would have been required to support, say, a high efficiency air-to-air heat pump solution (mini-split). We also looked at water-to-water (geo), but the source loop was crazy expensive due to poor soils, extremely high drilling costs, and hugely unbalanced annual cooling vs heat loads.

 

[Smooky]

I found this in the link below, it does a good job explaining it:

The German’s didn’t like the idea of recognizing the English BSP so they called their system DIN.
It is in fact exactly the same thread-form as Whitworth so to identify the correct thread size under the DIN Standard, you have DIN 15 equaling BSP half inch. DIN 20 equaling BSP three quarter inch and DIN 25 equaling BSP one inch.
Our dear friends the Americans went one better and they called their system NPT, National Pipe Thread.
Just as they changed the size of the Imperial gallon to the US gallon, they changed the thread-form from Whitworth to something entirely different. So instead of having the Standard 55 degree angle on the threads, they changed it to 60. (Yes you have to ask yourself why?).
The net result is that whereas the DIN pipe threads are interchangeable with BSP pipe threads, the American NPT pipe threads are not. You can graunch a half inch NPT into a half inch BSP fitting and the sealant will take up the slack.
However, three quarter inch and above in size that does not work, so you have to make up the correct type of adaptors.
https://www.harveywatersofteners.co.uk/blog/plumbers-pipes-and-german-vs-english-standards/

 

[Reach4]

I think that writeup missed the point that NPT is a also tapered thread and Whitworth is not. Tapering has some advantage for general purposes.

I thought NPT stood for National Pipe Taper or National Pipe Tapered. No? Wikipedia says National Pipe Thread.

 

[Smooky]

This is a UK artical so whoever wrote the artical may not know much about NPT. I think it answers the original posters question that DIN & NPT are not compatable except that 1/2 inch can be forced to work.

 

[Ginahoy]

I already knew DIN is different. My question is about DN vs NPT. DN is an ISO standard, not British or German. The chiller spec says connections are DN25. The importer says 1" NPT will obviously fit because they're the same thing. He seems to be implying that DN is the ISO standard for NPT, although I can find nothing online to substantiate that.

 

[Smooky]

Yea, I missed that somehow. This explains it:
http://www.engineeringtoolbox.com/nps-nominal-pipe-sizes-d_45.html

https://en.wikipedia.org/wiki/Nominal_Pipe_Size

 

[Ginahoy]

Thanks Smooky. Best I can tell, DN is not a pipe thread specification and is thus not sufficient to determine compatibility. Listing a fitting as DN25 would be the equivalent of an American spec showing NPS 1"

Since DN is a metric designation, it seems unlikely that whatever thread standard the chiller connections use would be compatible with NPT. Still, I have to wonder why the US distributor would claim otherwise. They've sold possibly hundreds of these in the US market.

Thanks for the help.

 

[BillTheEngineer]

There are adapters for go from DIN/ISO/BSP to NPT male female. NPT is common in North America. The rest of the world I would think DIN/ISO/BSP is, but it could depend on the application too.

http://www.hfifluidpowerproducts.com/general-metric-fittings.html

 

[Ginahoy]

@Bill, I called HFI and they only have zinc coated adapters, but the rep referred me to adaptall, which makes various brass and SS metric-to-NPT adapters.

Now that I'm armed with enough knowledge to ask the right questions, I can push the distributor to provide the actual fitting spec for the connectors. This particular model is ONLY sold in North America. I'm thinking the chiller actually has NPT connectors, and that the person who wrote the spec (DN25 1") perhaps didn't know what he was doing.