Lochinvar Knight 0-10V Boiler pump - how does it work?

Gman66

After kicking around the notion of replacing my old CI boiler with a modcon for the last 8 years, I am finally getting close to pull the trigger since my conventional water heater has a slow leak.

House is 2,900ft2 colonial in northern NJ: 185 ft of fin tube in two zones (first floor and second floor zones). Slant Fin app suggests 62K BTU design day, but HHD analysis suggests closer to 50K BTU. My calcs suggest design day return temp around 130*, so should be able to condense most of my gas bill.

Looking at Lochinvar Knight and I see that they now include a variable speed circ which is "controlled" by the boiler controls. It is unclear to me what logic is used to control the boiler circ to minimize the return temps which I see as the major drawback to P/S piping.

Using a reasonably accurate example from my house; if the outdoor temp is say 45*, the system temp requested by ODR might be 110* with a dT of 5* (about a 15% fire rate and 3 gallon flow in the system side). If I were to request a 20* dT in the boiler control, would the boiler slow the boiler circ so that it under pumped the primary (less than the system flow) and ramp the boiler supply up to 125* so as to maintain the system supply at 110*?

mattmia2

Someone here might know but this is a question for their tech support. Usually if you ask like that where it is clear you know what you're doing they will answer instead of saying talk to a contractor.

mattmia2

There may even be training material if you poke around in the section that is for professionals.

hot_rod

Someone mentioned @Heatmeister_2 maybe? that the V/S circ is no longer included or offered?

I have a Knight 55 in my shop and that is what it does, slows the boiler flow to keep the coldest return, or widen the ∆.

I have noticed that it does slow down warm up time if I try any setback on the slab.

If or when this circ fails I will go with a fixed speed ECM. I'd rather the power consumption savings of the ECM than the flow modulation.

109A_5

Hello @Gman66,
Not sure if they are using some sort of PID control (Proportional–integral–derivative controller) to get the temperatures where they want them to be.
0-10 VDC is just a fairly common analog control method quite often found with industrial motor controllers and other remotely controlled devices, there are others like 4-20mA, PWM (Pulse Width Modulation), etc.

0 VDC may be zero Pump RPM and 10 VDC would be full RPM, the heating system controller can probably set the pump RPM anywhere from zero to maximum, or any where in-between depending on the control voltage sent to the motor (the pump motor probably has its own internal motor controller).