[lotofquestions]

I am designing and planning to install a Lochinvar Knight WH085 boiler. The I/O manual indicates a option utilizing a low voltage output signal (BLR PUMP OUTPUT: Boiler pump speed output),it is wired to, and used to control the speed of a variable speed boiler circulator. Page 37 indicates that a (delta T) can be set to control the flow of the boiler pump.
The Service manual states the speed of the boiler pump can be controlled by the SMART SYSTEM control in order to maintain a minimum Delta T through the heat exchanger. Thus, as the firing rate decreases, the speed of the boiler pump can decrease as well. The SMART SYSTEM control outputs a 0 - 10V signal to the boiler pump to control its speed. The Boiler Pump Minimum Voltage parameter determines the minimum voltage given to the boiler pump, thereby setting its minimum speed. The range of this setting is 2.5V to 10V. The default setting is 3.5V.
I would like to implement a variable speed boiler pump. My goal would be to use the programmable features of the SMART system to define a Delta T to maintain. Basically I want to do the same thing a “Taco Delta T “circulator does, but have the Delta T programmable rather than fixed, taking advantage of the input and output sensors that already exist in the boiler. I can’t find any way to program a delta T parameter. Possibly the BLR PUMP OUTPUT is just a signal that’s value is directly proportional to the modulated fan speed. I don’t know. Can someone give me more detail on how this BLR PUMP OUTPUT is controlled?

 

[skippedover]

I'd use a delta 't' pump personally. Simpler and future potential problems are reduced.

 

[meplumber]

The 0-10 VDC output that you are referring to is primarily used in commercial and institutional applications where a building automation system is in place. The 0-10 VDC is a common signal for BAS that can be translated to a Variable Frequency Drive to modulate pump speeds.

This function is included on the Knight controls because the boilers can be linked or cascaded in commercial settings.

If this is a residential application, the cost of an automation system to translate the VDC signal and the corresponding VFD would kill you.

A fixed Delta P or Delta T circ is your only option unless budget isn't a factor.

 

[hearthman]

stakrellis, This is the Ask Our Pro's or AOP forum. In order to post responses here, you must have verified qualifications and have been approved by the AOP Committee. Please see my signature line for links to register and review the AOP Forum Rules. Thank you. Your post will now be deleted. Further infractions may result in loss of posting privileges.

 

[lotofquestions]

Thanks guys,
I will probably go with the Delta T pump. I am just tring to convince myself that I am not missing a more elegant way of implementing delta T control utilizing the SMART system. There are a number of varible speed pumps that can be controled directly from a 0-10 volt signal. I would hate to find out after the fact that I had this great feature but I did not know how to use it.

 

[skippedover]

meplumber explained it well enough. The 0-10V signal does not initiate in either the Knight boiler control nor at the pump. It initiates at the building/system control and is fed to the boiler and thence to the pump. Look at the Knight website and you'll see a sample of 15 or so boilers all linked together in cascade form. That's what he's talking about and where the 0-10V signal would be used.

One more thought. I'd recommend the Delta 'T' pump for the secondary loop only and let the boiler modulate the flame to maintain boiler temps. You're in for a rough ride if you try to decrease the flow through the boiler without direct control over the staging. All low mass boilers are critical on water flow rates and require specific pumps to provide that flow. I believe your Knight boiler came with the proper pump for the primary loop. That is the pump you should use.

 

[lotofquestions]

I am very happy to have someone to speak with on this subject. This is great. I think I needed the combination of both you guys to get my head around this concept. Thank you. Again
I would like to ask another question. Is it ok to just continue with this post or should I start another post? What is preferred?
Anyhow. My question is.
My residential system details, 1960’s, 1900 square foot ranch house, 60,000 BTU heat load, Loads of copper Slant fin style baseboard radiation , 3 zones all about equal, propane. Lochinvar Knight WH085 with 40 gal DHW.
Skippedover, you are correct that the boiler did come equipped with a pump ( Grundfos 3 speed). You mention primary/ secondary piping. So I would like to hear what you think about this approach to this system.
I do not plan on using primary/secondary piping. I plan on using a configuration like page 45 of the I/O manual. Single Boiler, Full Flow –Single Temperature -zoned with zone valves, DHW priority. The boiler circulator would be a Taco 008 Delta T. I believe that circulator will allow me to keep the boiler in the condensing range most of the time.
If you get a chance look at this report I found on the web: New York State Energy Research and Development Authority Final Report August 2011: Condensing Boilers and Low-Temperature Baseboard Convection. (I will summarize…. In a existing house with a adequate amount of base board radiation, it was found that primary/secondary piping caused the temperature of the return water to be too high to condense most of the time. Elimination of the primary loop solved the problem.)
Your thoughts?