Lochinvar knight KHB085N with ECM pump P/S vs direct pipe

[Robert McCallum]

With the new Lochinvar knight fire tube boiler and the ECM pump is there any benefit to using a primary secondary loop vs piping direct to the zones with zone valves. I am trying to get the lowest return temp and long run times without using the extra power that primarily secondary pumps use. I have three zones and one indirect hot water zone. The zones are cast iron rads supplied by manifolds so flow to each zone can change to accommodate the minimum flow of the boiler and not affect the heat balance in the house. My concern with the P/S loop is hot boiler water returning to the boiler raising the return temp and cold water returning to the system lowering the system temp. Lochinvar claims that it ok to use direct piping and their install manual shows it but I don’t know which way is best. I know how important P/S piping is with some boilers and why it is used but I don’t think it will give the lowest return temperature.

 

[Dana]

If the flow math works and Lochnivar now claims it won't void the warranty (like they used to), go ahead and pump direct.

P/S always increases the EWT at the boiler, and lowers the temp of the water going out to radiation- it's always an efficiency hit with a mod-con.

 

[Sponsor]

 

[Ekubec]

Resurrecting older post.... Curious about the delta t function of the knight boilers when piping these direct. I am looking to design a small system with one large 'always open' zone (e.g if heat is called for heat will always be supplied to this zone as there are no zone valves on it ) and want to use delta - t and direct piping. I believe I read in a lochinvar manual that the delta t function of the knight boiler can only be used in a primary/seconday setup. I am curious if anyone has set up these knight boilers with delta t in a primary system. I understand that a primary secondary system ensures that there is always open flow to the heat exchanger as long as the pump runs. But it would seem in my set up that condition is also met with its always open design

 

[Fitter30]

What model Knight?

 

[Ekubec]

What model Knight?

WHB (055N or 085N)

 

[Fitter30]

All three boilers khb085, whb 055 - 085 use the same pump.

Knight Fire Tube Boiler | Residential Boilers | KNIGHT™ Fire Tube Boiler | Lochinvar

Go to tech documents then literature the typical specs
Pump grundfos upml 25-10
Khb 35° temp diff 3 gpm , 20° 5 gpm
Guess u need to figure out ur head and gpm
All three boilers 1" water connections. For my 2 cents primary/ secondary loop with a ecm system pump. Boilers are low flow vrs your systems.