Variable Circ boiler protection ?

[Bricks]

In Hot Water set up his system with variable circ boiler protection. It makes sense to me what are your thoughts on setting up boiler protection this way?

More information .......I tried to attach his setup and tech information, IHW made in the post titled Circulators and Air Eliminators. I could not get it done.

 

[Jackpine Savage]

I'm about to finish my Tarm boiler piping and this has gotten my attention too. I had planned on a Tekmar 156 to control the boiler and using the Termovar as supplied by Tarm for boiler protection. This morning I was looking at the Tekmar 356 that In Hot Water mentioned. I don't see any differential function, unless I missed it. I'm wondering if it would make sense to use the Tekmar 156 to drive the 356. It would be about $400 for the two units.

 

[pybyr]

If you're starting to get into many hundreds of dollars on controls just for the boiler- start looking at Nofossil's control system-- which can handle not only the boiler, but other parts of the system as well.

 

[sgschwend]

Isn't using a mixing valve the same thing?

Or are you concerned about over temperature?

 

[Nofossil]

This is an interesting topic. As best as I've been able to figure it out, there are two separate objectives, and numerous overlapping techniques to accomplish them.

Objective #1: Don't introduce water into the boiler inlet that's less than about 140 degrees (to avoid boiler condensation damage).

Objective #2: Produce water at the boiler outlet that's at a desired temperature - 180 degrees, for instance (may be different values in different situations).

As far as I know, the only basic way to meet #1 is to recirculate water as needed from the boiler outlet directly back to the boiler inlet. I use a zone valve, Econoburn uses a circulator, and there are various types of mixing valves that can serve the purpose. If using a bypass valve or circulator, modulating it would provide better control. However, I doubt that this is an area where really fine control is really necessary. I suspect that brief excursions below 140 aren't going to cause a problem.

In addition to recirculating, you can also turn on zones sequentially to minimize the 'slug of icewater' problem.

All of the techniques that address objective #1 also have the effect of raising the boiler outlet temp, which usually helps with objective #2. Besides inlet temp, other factors that affect boiler outlet are the phase of the burn, the blower speed, and the flow rate through the boiler.

You can't do much about the phase of the burn, but there are three things that a good control system could do:

1) Estimate the desired boiler BTU output and modulate the blower(s) to try and achieve that value (or as close as possible given the constraints of the burn phase)

2) Balance, prioritize, and sequence heat loads to present a relatively even heat demand to the boiler

3) Modulate the boiler circulator to achieve the desired outlet temperature.

Built-in boiler controllers like the EKO don't do this. Instead, they modulate the blower to try and achieve the desired outlet temp. That's a reasonable approach, but it means that the blower starts to slow as you start to get close to your desired temp, and stops if you reach it.

What you really want is a balanced situation where the boiler is producing the right amount of heat (say 60,000 BTU/hr) and the combination of zone return temperature and flow rate is such that the boiler outlet temp is at 180 degrees. If the outlet temp starts to climb, then the controller should increase the flow rate and/or open another zone.

I don't do all of this as scientifically as I could, but I do make an effort. For instance, I currently have a three speed circulator and I control the circulator speed to try and match the boiler output. I don't control the boiler blower, but I manage loads and circulator speed to try and keep the boiler outlet temp just below the point where the EKO controller will shut off the blower.

I also prioritize and sequence loads:

- If DHW is close to being cold, that takes precedence over everything else.
- If someone wants to use the hot tub, that's the next priority
- Heating upstairs living space
- Superheating DHW
- Basement heat
- Heating the hot tub (without a user request)
- heating storage is last

 

[RobC]

Using a mixing valve or variable speed circ's achieves the same purpose, temper the return water to the boiler so the boiler never sees inlet water temps below 160F or 140F ( thermal shock ). However the two plumbing layouts differ and allow for positioning of components, of the system, in different positions. For example the plumbing layout using variable speed circ's allows for ideal placement of the air / water separator. I run a Tarm. In the paper work that came with the boiler there were multiple notices that addressed the use of a mixing valve and warranty. As an alternative, BIOHEAT has started selling the Ladomat mixing circulator that is an all in one unit, circulator and mixing valve.

The second part of all of this discussion is the energy consumed with the increased head / friction of these valves, which, the variable speed approach minimizes.

 

[DaveBP]

BIOHEAT has started selling the Ladomat mixing circulator that is an all in one unit, circulator and mixing valve.

They sell the ACASO equivalent to the Termoventiler's Ladomat. They call it the Termovar loading unit.

 

[Bricks]

This is an interesting topic. As best as I've been able to figure it out, there are two separate objectives, and numerous overlapping techniques to accomplish them.

Objective #1: Don't introduce water into the boiler inlet that's less than about 140 degrees (to avoid boiler condensation damage).

Objective #2: Produce water at the boiler outlet that's at a desired temperature - 180 degrees, for instance (may be different values in different situations).

As far as I know, the only basic way to meet #1 is to recirculate water as needed from the boiler outlet directly back to the boiler inlet. I use a zone valve,

When controlling boiler inlet temp with a zone valve are you placing an aquastat before the circ pump..OR???? How are you closeing the zone valve when temp is up?

What you really want is a balanced situation where the boiler is producing the right amount of heat (say 60,000 BTU/hr) and the combination of zone return temperature and flow rate is such that the boiler outlet temp is at 180 degrees

How well do some of the new circ pumps that sense load changes as zone valves open and close and are self modulating work? Once the boiler is up to temp can these circs be set up to maintain correct flow and temp in the system?

Just another question just out of curiosity does it make a difference if the boiler circ pulls or pushes water through the boiler?


l.

.

 

[Nofossil]

When controlling boiler inlet temp with a zone valve are you placing an aquastat before the circ pump..OR???? How are you closeing the zone valve when temp is up?


How well do some of the new circ pumps that sense load changes as zone valves open and close and are self modulating work? Once the boiler is up to temp can these circs be set up to maintain correct flow and temp in the system?

Just another question just out of curiosity does it make a difference if the boiler circ pulls or pushes water through the boiler?

I personally measure the boiler inlet temp to control the bypass zone valve.

I don't know how well any commercial self-modulating circ pumps work - I have no first-hand experience. I assume they work fine, and I believe they are usually set up to vary speed to try and control a temperature measured at some other point in the system. They are a bit pricey, but they have the potential to really fine-tune system performance. Of course, it adds more complexity to the system.

As with many things, I'll do it myself. I'll pretend that my solution will be cheaper, and in the end I'll spend more money and far more time than if I'd bought the commercial solution. Once I get it figured out, I'll sell it at a loss to show how clever I am ;-)

Current thought is to pump away from the boiler, but in most systems I don't think it makes much difference.


The graph shows my bypass valve working (green line near the bottom) to try and keep the boiler inlet above about 57 degrees C (135 F). The recirc valve is open for a little while as the fire starts. It's closed while the boiler heats the house, DHW, and hot tub. Once those loads are satisfied at around 8:30, the storage (tank) zone valve opens and we start seeing cold water at the inlet. The recirc valve is open a high percentage of the time for the next couple of hours until the bottom of storage gets hot enough at around 10:30. The recirc opens again as the fire dies out.