Safe to run w/o Termovar?

[BoilerMan]

Hey guys,
As some my know, I'm buying an Attack DP45. My current setup is primary/secondary with zone valves to control all loads, accept the injection loop for radiant slab, which is closely spaced tees in the primary loop. Under all conditions the return water will never below 155 at worst case with all zones open (which never happens), it is usually in the 160-170 region. I ask because most on here seem to have them. When the boiler is comming up to temp and the primary pump has not yet started and the boiler reaches the preset, there is about 3 gallons of room temp water dumped into the boiler and things begin. Is this a problem for a gasser??? Or is the concern a sustained low return temp causing tarring? I just don't want to cause thermal shock to anything. I have low return temp inherrantly built in through control, but is a Termovar still necessary for this initial slug of cold water? I want to have one ordered in time to get things piped up.

Thanks
Taylor

 

[DaveBP]

The water coming back from a concrete slab can be a lot cooler than 155F, Taylor.

If you are sure there is no combination of circumstances that would allow water cooler than about 140F to return to the boiler for a continuous period then I suppose you could get away without any other return protection. Put a thermometer in the return pipe just before the boiler (in the water stream) and check it whenever you walk by to make sure.

The danger is not "thermal shock" (still not sure what that is) but slow and steady condensation in the exhaust stream before it gets out of the boiler. It's very acidic water that comes off the exhaust and it can and will rot out the steel. Thermostatic valves are overpriced (I think) for what they are but are priced according to the consequences of not having something that will always protect your boiler under all circumstances.

 

[stee6043]

Not worth the risk. Danfoss valves are cheap compared to a new boiler...

 

[BoilerMan]

The danger is not "thermal shock" (still not sure what that is) but slow and steady condensation in the exhaust stream before it gets out of the boiler.

Thermal shock is like dropping a hot frying pan into cold water, things can crack. I was worried if this would have any effect on the refractory, but I guess it is nowhere near the water jacket. It's just the initial time when the primary pump comes on and a cold 3gallon slug comes from the 1 1/4" primary loop I was worried about. No sustained cool return water here.

Thanks guys for your input.
Taylor

 

[ewdudley]

begin. Is this a problem for a gasser??? Or is the concern a sustained low return temp causing tarring? I just don't want to cause thermal shock to anything. I have low return temp inherrantly built in through control, but is a Termovar still necessary for this initial slug of cold water?

You might well be fine if all is as described, thermal shock is more of a concern for cast iron components.

But it's hard to tell what you're describing without a schematic. Is there a loop that pumps around and around through the boiler that circulates even when no load is drawing heat?

 

[BoilerMan]

Yes, I have a Taco 0010 circulating through the boiler and a total of 30' of 1 1/4 copper with closely spaced tees to all loads. When the boiler reaches 160 an aquastat turns the 0010 on, and powers up the controller for the rest of the system. This way if there is no fire: no heat in the boiler: therefore no power to anything having to do with the heating system.

I think I have the answer to my question,
Thanks for everyone's time.
Taylor

 

[Armaton]

Taylor,

Have read both your threads several times. I still don't see where u are getting the 160 degree return water from after the initial 3 gallon slug of cold water. With only 114 degree water pumped to your slab, there is "NO WAY" you will have 160 degree water for return, unless something else is going on that you haven't expressed in the threads. What is the inherent low return temp via control? Is it because your heating loop is so small with so small of a temp drop through it that the hotter water will always offset the 100 degree or so water from the slab?

 

[BoilerMan]

Taylor,

Have read both your threads several times. I still don't see where u are getting the 160 degree return water from after the initial 3 gallon slug of cold water. With only 114 degree water pumped to your slab, there is "NO WAY" you will have 160 degree water for return, unless something else is going on that you haven't expressed in the threads. What is the inherent low return temp via control? Is it because your heating loop is so small with so small of a temp drop through it that the hotter water will always offset the 100 degree or so water from the slab?

Ok, lets do the numbers. If I dump 60,000 btu/hr in the slab I'd need a T of 50 @ 2.5GPM, this is in the closelt spaced tees.
So, if the primary circ is a 0010 it's pushing about 14GPM through the boiler and the primary loop. 14 GPM of 180 water mixed with 2.5GPM of 130 (180 - 50) gives us 170 return water.

The math proves it, remember there is only a small amount of cooler water comming from the injection loop which mixes a little (2.5 GPM in this example) 180 degree water with the 90 degree water comming from the slab to bring it up to 114 degrees. I"m not shore how else to explain it, it's closely spaced tees (actual ones shown in first pic above) small amount of cooler water mixed with large amount of hot water = water above 140 in all cases. All of this assumes a boiler can supply 180 water, it's when we pull so many btus out that the supply temp drops and things go downhill in a hurry. Thats why I set the aquastat on the boiler to turn everything off if the supply cools to 160 then the fire heats everything up before more btus can be pulled out of the boiler again. (Bang Bang control), but if all is well (and I build a fire often enough) there is never enough btus pulled out @ 114F slab injection to make this happen.

 

[ewdudley]

...

The math proves it, remember there is only a small amount of cooler water comming from the injection loop
...
Thats why I set the aquastat on the boiler to turn everything off if the supply cools to 160 then the fire heats everything up before more btus can be pulled out of the boiler again. (Bang Bang control),
...
f all is well (and I build a fire often enough) there is never enough btus pulled out @ 114F slab injection to make this happen.

Sounds like you've got it under control. With a primary loop going through the boiler and enough flow to overwhelm load flows, then bang-bang works perfectly. Just because it's simpler, more reliable, meets the requirement, and is less expensive doesn't mean it's not better.

I wouldn't be surprised if the 0010 would pump something well over 20 gpm through a short fat loop, which might be overkill and an unnecessary electrical expense. A plain old 007 might pull 12 or 14 gpm and would draw one third the power.

An enhancement you might like would be to add an aquastat on the return side of the boiler that would disable all loads when return temperature is too low, then the primary loop pump could continue pumping and avoid slugs of cool return water. The boiler's supply temperature control would run the primary pump and the return aquastat would enable/disable all the loads.

Also, the DP45 specs a 65 degC/149 degF minimum return temperature. I doubt it would affect your plans, just a heads up just in case it would.

 

[DaveBP]

I would still put a calibrated (put it in boiling water on the stove) thermometer inside the return line just before the boiler.

Nothing so heartwarming as seeing your theoretical analysis in action and knowing you got it right.

 

[Armaton]

Maybe I'm just thick!

But how does the startup overwhelm a 115 gallon buffer tank after 2.5 gallons, or is it closed off from the system unless you leave for an extended period? I understand the "Bang Bang", but won't there be a lot of short cycling untill the buffer is up to temp?

 

[ewdudley]

Maybe I'm just thick!

But how does the startup overwhelm a 115 gallon buffer tank after 2.5 gallons, or is it closed off from the system unless you leave for an extended period? I understand the "Bang Bang", but won't there be a lot of short cycling untill the buffer is up to temp?

There's no buffer in this case, just a 30 ft primary loop of 1.25" copper going out and back from the boiler, which the loads pull from through closely spaced tees.

With and estimated 12 gpm going round and round the primary loop, entering at 160 degF, it would take three parts 160 degF water and one part part 80 degF to maintain 140 degF return temperature. If the three-to-one ratio is maintained then everything is fine until supply temperature drops below 160 degF, at which point need to either stop the primary loop and let the boiler recover, or stop the loads from injecting cool water until the boiler recovers while the primary loop keeps circulating. In either case the boiler recovers using bang-bang control to stop the flow of cool water into the boiler loop.

It can only work if there is a recirculation loop from boiler supply to boiler return and the flow is sufficient to mix supply temperature up to minimum return temperature.

 

[Armaton]

Eliot,

I understand the theory and the numbers, but in his original post he said, " I have storage in a 2,200 ft2 8" thick slab with the tubing about 6" deep (on purpose), and a 115 gal. indirect water heater so I can go for several days w/o a fire." That lead me to beleive that it was a buffer/storage situation. So the 115 gallon tank is a zone and isn't always open to the system? Help me understand. And as u know I need a lot of help!

 

[BoilerMan]

I would still put a calibrated (put it in boiling water on the stove) thermometer inside the return line just before the boiler.

Nothing so heartwarming as seeing your theoretical analysis in action and knowing you got it right.

Whew...... This is going along.........

Ok, I have a thermometer on the boiler return, this is how I know the numbers as stated, never going below 155F.

EWD is correct, the indirect is not a buffer tank, it is a zone all by itself.

Also EWD, I like your idea of cutting the load (powering down the ZV controller in this case) w/o turning off the primary loop to let the boiler recover. I'm a fan of the simpler the better, the more reliable the better, but sometimes the more difficult to come up with.

The slab mixing station (which is fed from the closely spaced tees in the pic, also it's a Taco radiant mixing block pictured in my avatar) is set to 114F fixed injection temp. This pulls about 60,000 - 80,000 btu out of the loop (keeping the return temp above 165 as we did the math, and as I've seen on the thermometer.

I didn't want to get into all of this but hopefully it helps someone with their install.

EWD, the 0010 would push A LOT of water through the primary loop, but I wanted to eleiminate as many circulators from the system as I could, saving wattage, the 0010 is 126 watts, 007s are 81 watts. So I went the unconventional way, and modified some things. This may be confusing to some but here it goes.

I took apart a regular Taco 1 1/4" cast iron weighted flow check and removed the brass weight (pictured) and machined a new one out of solid brass round stock (don't have a pic) which is twice as heavy. This creates a 4psi pressure drop on the loop which brings the 0010s flow down to around 14 GPM. The reason I did this is now I can use zone valves (low power draw) on a primary/secondary setup. The only closely spaced tees are the ones pictured which feed the injection loop for the slab (the main draw), and the dump zone (unit heater in garage, never used). You can see in the second and third pics the top of the indirect and it's 1" zone valve (Caleffi Z-One). The unused ball valves are for future input/output. This is not conventional, and was an expierement, which has proven to work well, allowing my preferred zone valve setup without sacrificing the benifits of primary/ secondary pipeing. I have some small panel radiators on the second floor in the bedrooms and didn't want a dedicated (read: watt hungry) circulator for each one, now I use less that 150 watts to run the whole thing which is less than two 007s. I hope this helps quell all of the unclear words and puts a picture to some of it.

This forum has helped me to think out of the box and hopefully I can inspire someone else to do the same.
Taylor

 

[Armaton]

Taylor,

Thanks for the schematic, clears up my confusion. Do you have other DHW than boiler supplied, or do you burn during the summer also?

 

[BoilerMan]

Taylor,

Thanks for the schematic, clears up my confusion. Do you have other DHW than boiler supplied, or do you burn during the summer also?

I use a Toyotomi Oil Miser 180 to directly heat the DHW in the summer. It's switched at all hot water outlets (faucets). It will give hot water from a cold start in about 15 seconds. Then it's turned off via low voltage wireing connected to the "timer" input on the control board. This way it runs as a cold start direct hot water heater, no standby losses.

I'd like to so some type of solar, possibly coils of poly pipe in the attic circulated through the extra coil in the indirect to preheat the water going into the Toyotomi.

Taylor

 

[ewdudley]

Whew...... This is going along.........

the 0010 would push A LOT of water through the primary loop, but I wanted to eleiminate as many circulators from the system as I could, saving wattage, the 0010 is 126 watts, 007s are 81 watts. So I went the unconventional way, and modified some things. This may be confusing to some but here it goes.

I took apart a regular Taco 1 1/4" cast iron weighted flow check and removed the brass weight (pictured) and machined a new one out of solid brass round stock (don't have a pic) which is twice as heavy. This creates a 4psi pressure drop on the loop which brings the 0010s flow down to around 14 GPM. The reason I did this is now I can use zone valves (low power draw) on a primary/secondary setup.

Neat, I didn't appreciate how much more efficient a larger pump could be.

Result may be more conventional than you think, I believe there are purpose-built hydronic pressure regulating valves available for the purpose of bleeding excess pressure from a supply manifold to the return side, normally to prevent high flow velocities through load circuits when a fixed-speed pump is feeding multiple zones. Nevertheless you'd still need a bigger pump to flow 14 gpm at 4 psi pressure drop.

I suppose state-of-the-art might be to have a small dedicated pump for the primary loop with a separate constant-pressure ECM pump to feed the zone-valved loads, but then you'd have the expense of two pumps and not much of a power savings to show for it, so I'd say that's a pretty good answer you have there.