Boiler Control/Indoor Reset Question

AlaskaDick

I am in the process of slowly replacing a Weil-McClain CGs Gold cast iron boiler using outside combustion air with a Lochinvar Noble NKC150N mod-con with a 10:1 turndown ratio. At the same time I am replacing the baseboard heat with staple up with heat transfer plates and some radiant wall. The garage slab has imbedded tubing and uses a mixing valve and circulator. DHW is by an indirect water heater.

The new system will have primary and secondary loops and a single delta P system circulator. Approximately 2/3 of the floor area is in three zones controlled by zone valves and thermostats. The remaining 1/3 is several smaller zones with TRVs and wall mounted TRV remote operators.

About 15 years ago I upgraded the boiler control to a Tekmar 260 to get outdoor reset and it has served me well. It also has a capability for indoor reset which I never looked into. A Taco ZVC404 expanded the number of available zones.

The Nobel has internal outdoor reset, but not indoor reset. Can the Tekmar and Nobel combination be configured to provide both outdoor and indoor reset? Are the advantages of indoor reset worth the extra complexity and effort? To support all the valves I will need to use a controller. My options are to use either the Tekmar or Taco as both (as well as an extra Taco) are on hand.

Location is Anchorage, Alaska. Published design temperature is -20f, but we haven’t actually seen anything below -15f since 2009. High temperature rarely exceeds the high 70s. The space is occupied essentially 24/7. The space is well insulated and sealed and has an HRV. The living room has large windows on two sides, including a south facing wall that gets low angle sunlight during the winter. Last year I added a hydronic booster coil and TRV to the duct from the HRV to temper the fresh air to the house because the fresh air to the rooms could get below 60f on a really cold day.

EdTheHeaterMan

I am not familiar with the concept of indoor reset. I need to look that up.

11 minutes later:

OK this is a concept that uses modulating energy input based on keeping a constant comfortable temperature inside the building.   I have heard of heat pumps and air conditioners with variable speed compressors and modulating gas valves on boilers to keep the building from larger temperature variations associated with on/off thermostat operations of conventional HVAC equipment.   I have installed many of these items for myself and for customers,  I just never used the term Indoor Reset to refer to this concept.  It is almost like “AI”. I prefer Actual Intelligence over Artificial Intelligence when it comes to this new stuff!   

EdTheHeaterMan

So the outdoor reset is part of the Tekmar control system.  The Lochinvar Noble has the modulating gas valve built into the system. So you are already 80% there even if you don't add anything to the control system other than the boiler demand input from the Tekmar demand terminals to the boiler. Now if there are more sensors that can hone-in to the room comfort settings so the gas valve has more precise control over the boiler temperature, then that is even better!

EDIT:  The Lockinvar has no mention of indoor reset in the I/O manual. That said, the concept of indoor reset is not commonly called indoor reset.  The fact that the boiler modulates based on the input from supply and return water temperature sensors built into the boiler, along with the outdoor sensor will, by its design, be functioning as the "indoor reset" you are looking for.  The input from the Tekmar boiler demand will not get satisfied as quickly as the on/off Weil McLain boiler you are replacing.  That is because the Lockinvar will not make the water temperature hot enough to cause the boiler demand to be terminated by the Tekmar. 

 In fact, the features of one ODR operating in conjunction with the other ODR may actually be redundant.  If the boiler ODR is set to a reset curve that causes the boiler to produce 120°F water to the heating emitters, and the Tekmar is set to a reset curve that only requires 119° water temperature, then there will be some on off cycling albeit few and far between.  If the opposite settings happen to be selected, then the Tekmar will never get enough hot water in the heat emitters to be satisfied in order to cause a stop of the demand for heat from the boiler.  

The redundancy will not fight each other, but actually makes one of the controls unnecessary.  

The bottom line of the ODR is the water temperature in the heat emitters.  When the WM made 160° water and the heat emitters only needed 120°, the Tekmer would shut down the WM until the system water temperature dropped below the 120° requirement.  The boiler would fire with 100% of the firing rate of the boiler’s burners. When the emitters got the right amount of heat the Tekmar shut down the WM.  With that old boiler you get all or nothing and the Tekmar did the modulating by shutting off the burners as needed.

With the Lochinvar The gas valve will do the modulating as needed. 

In short: you don't need the Tekmar 260 with the Lockinvar Noble NKC150N mod-con with a 10:1 turndown ratio

hot_rod

John over at Exquisite Heat is a proponent of the indoor reset function and has built controls with this tech.

Mike from Missouri had a good explanation

fentonc

I don't want to hijack the original thread too much, but I came up with a similar 'indoor reset' scheme for my Boilertron controller this season (it's controlling a very oversized CI boiler driving 3 oversized zones of fin-tube baseboard) - the general idea is to modulate the aquastat differential based on the worst-case thermostat duty cycle. So it runs with a high-limit of 180F, but when it's warm out, it will let the SWT drop all the way down to 120F before firing again. As the fraction of on-time for the thermostat increases, it can raise the average SWT by raising the temperature floor in the aquastat.

We actually had a cold snap yesterday that momentarily hit the design temperature, and it still had no problem recovering from overnight setback even with the differential still at 60F.

hot_rod

this Idronics issue covers some if the more sophisticated control logics P, PI, PID used in hydronics controls

Tekmar also has papers on these logics and how their control use the various methods

Eastman

@AlaskaDick

Some mod-cons allow for a separate control system to more or less directly control the percentage burner rate of the boiler. However, you need both a control system and a boiler that supports a common modulation interface. The Tekmar 260 is a single stage control and only provides on/off boiler commands. Also, even if you had such a controller, I do not believe the Noble is capable of receiving modulated firing rate commands. You would need the Loch Knight and a more expensive Tekmar modulating controller. As such, I believe the 260 is completely redundant in your new setup with the Noble. The Noble has outdoor reset, and rate and ramp limiting.

You mentioned the optional indoor feedback of the Tekmar 260. This seems like a strange feature to me on the 260, mainly because the 260 is not aware of the desired room temperature programmed into the calling thermostats. Ideally the controller would read the desired and actual temperatures from each zone, and in conjunction with the outdoor temperature, an appropriate water supply temperature is then calculated. As an example, there are Tekmar tn2 and tn4 communicating thermostats that can relay this information. But the boiler control also needs to be a fancier Tekmar model that can work with either the tn2 or tn4 communication protocols.