Raypak boiler settings mvbIV

aircooled81

I was never able to locate a detailed description other than the IOM and Versa control IOM for Raypak MVB IV boilers.
I have managed to over think some parameters, and would like some input regarding the theroy behind some of these:
Setpoint- this is the temperature the boiler will try to maintain, based on the location of this sensor in the loop. does anyone know how the boiler identifies the correct firing rate to maintain this, wether it's 20*F from setpoint, or has over shot setpoint?;

Target Max - Maximum Target Boiler temp that the boiler can be set to. Is this only regarding outside air set back? or does this lock-out the setpoint adjustment from raising above this point? I originally thought this was the hottest the boiler discharge would be, but that has proven to be incorrect;

Target Min - just like Target Max but the low end. does this just lock out the lowest setting for the setpoint to be manually changed to? or do both target max and min play a roll in the boilers firing rate and temperature adjustment itself?;

Differential - two ways, automatic, or select manual from the PIM - first of all, is this just the deadband the boiler will operate between to maintain the setpoint for the sensor?
Is there a maximum and minimum differential the boiler will maintain while in auto? is this pre determined or a fixed algorythem? do changes of other settings assist in the boiler determine it's differential? it appears in auto differential the boiler stays on longer, maybe it changes this up and down to keep the boiler on for a longer period of time?;
in cascade setting - when the boiler is the master, and it has a follower, what does it need to do to bring the follower on? basically I have seen the follower only come on when the master gets to 100% capacity for an unknown amount of time... but I have also seen the follower start an ignition cycle only to be stopped by the master as it no longer needs the assistance. So is there a way to bring the follower on below 100% master, or prevent premature firing of the follower?;

Outlet Max - this is adjustable, but on my MVB's I have found the display never holds an adjustment below 30*F. I have also noticed that the boilers seem to overshoot this often, and not slow down the firing rate when we approach outlet max. This leads to automatic high limit trips sometimes. Does the boiler have a setting to make it respond to outlet max sooner, to dial down the gas rate faster, so it does not overshoot? I have visually monitored the boiler outlet temp continue to climb past the max, and the boiler still increases the gas valve output, as the setpoint sensor in the secondary loop has not reached setpoint;

Mass - thermal recovery. there have 2 options, 1 is for fast response. what are the 2 best determining factors in your system to utilize the mass function. most of my boiler loops consist of a primary and secondary loop, inwhich we have multiple boilers on the primary, and the secondary loop has one or more pumps that adjust (VFD) speed based on pressure differential 2/3rd of the way out in the loop. so in some circumstances the flow in the secondary loop can close down to much lower flow than even the primary pumps on the boilers;

to curtail this issue with overshooting the boiler max, and tripping auto hi limit resets, we have opted to install buffer tanks. is there anything that can be done to the boiler settings to prevent this if a buffer tank has not been installed. It's become very apparent, with low to no flow in the secondary loop, the boilers will consistently fire and overshoot tripping themselves, because they do not react quick enough to returning hot water.

swampcooler101

Do you have a primary secondary system?

If so what is your minimum flow on the secondary side. Sound like you need to move more water.

aircooled81

ahh, very insightful question SCooler101
the system is a primary secondary for reheat coils on vav boxes. the most common application we use is a fixed 180*F setpoint for the secondary loop, 2 ways valves (sometimes a few 3 way valves to maintain constant flow) and a differential pressure sensor 2/3rd of the way out in the secondary loop to monitor differential pressure. as the differential pressure climbs, the secondary pumps slow down. as the diff prsr lowers, the secondary pumps speed up.
I do not think a minimum flow exists, as the pumps do not maintain flow, just differential pressure. I would have to do some engineering and mathematical review of the loop and associated components to figure the flow at specifically maintained differential pressure.
Raypak tech support told me the secondary loop flow should not slow to lower than 110% of the primary pumps flow. so if my primary pumps move 40gpm, then my secondary pumps should not slow to more than 44gpm. I am sure my secondary loop slows more than 44gpm. In this instance they are 75gpm pumps, and slowing below 50% quite often.

do you think, that even if my secondary loop has not reached setpoint, I should disable the boilers if the secondary loop is not moving more than 110% of the primary loops pump volume?
wouldnt that prevent me from achieving design secondary loop temperature?
I sure wish there was a way to make the boiler output less btu's when the secondary loop was below 110% of primary loop flow.

swampcooler101

This may be a stupid question but.... Isn't one of the features of a primary secondary hot water system the ability to flow backwards through the decoupler?

aircooled81

ahh, there are no stupid questions swamp cooler 101, just long winded answers like this one...
the decoupler is the point where water can flow two opposing directions in the same pipe.
As water moves through the secondary loop, it is applying a volume. lets call that a fixed number like 100gpm. now the primary loop is also outputting a volume, lets give that a fixed number like 50gpm.
now heres where the magic happens. as long as the flow from the secondary loop allows, the flow from the primary loop trades water. its a natural fact, when water leaves one loop to join the other, something has to take it's place.
so as long as the secondary loop wants to move 100gpm, it will put some of that into the primary loop. why you ask, well because the primary loop is trying to move 50gpm, it has to go somewhere. so it creates a slight pressure difference with it's pump, this is the void in the decoupler. at that 'void' the primary loop fills it with 50 gpm, and send it's other 50gpm down the secondary loop. now the primary loop is sending all of it's flow out into the secondary loop, and the missing water is being replaced by the returning water from the secondary loop.
but lets say the secondary loop wants to move less water, maybe 3/4 of the valves in the secondary loop start close. well 25% of 100 = 25gpm. so now the secondary pump is only circulating 25gpm, but the primary loop doesnt care. the primary loop stil wants to put 50gpm somewhere. so it puts 25gpm into the secondary loop, but has to send the rest back through the decoupler to join the secondary loops return.

as my hero mr holohan would put it, "can you see it in your minds eye?"

I guess its not magic, its the law of nature. and the only real stupid question is, the question that was never asked.