TRV's, circulator and Tekmar 260

Tristan

I'm retrofitting my steam cast iron radiators to FHW. I want a simple but reliable system(similar to attached photo). After reading a lot of threads about TRV's, home run pipping and manifolds, I have a few questions.  My boiler is a Burnham Revolution RV5, currently with Taco switch relay 2 zone (thermostat from old system and DHW).

Now, I'm running 1/2" Pex-Al-Pex home runs pipping from manifold to 8 radiators. All radiators will be controled by Danfoss TRV's.

I'm thinking of using a Tekmar 260, with outdoor reset as a boiler control device. Should I bypass the Taco switch relay? What about my DHW, will it also be totally  controlled by the Tekmar 260? I'm using a Groundfos Alpha circulator. My understanding is with this pressure regulated circulator, I don't need a differential pressure bypass valve on the manifold. Is that correct? 

Should I bother putting a dirt separator (Spirotrap) knowing

that the radiators are steam converted to FHW, with potentially a lot of

sediment and rust? Before turning the system on, should I flush the system with some cleaning agent?

My old school plumber doesn't understand what I want to do. He thinks I'm nuts and my supplier is not very helpful either.  So I guess I need a little help.

Also, Is there anyone from Boston-Cambridge area that knows about modern retrofit of cast iron radiators?<span style="font-size:12pt"> </span>

Crunch

Try tk03

You might want to try tk03 at http://www.hvac-answers.net. He's in PA, but may know quite a bit about this.



Crunch

gennady

TRV

If you are using TRV with standard efficiency boiler you do not need outdoor reset, because you will make boiler condense and it really does not matter, because TRV will do the job. If you still want outdoor reset, then you have to do it with diverter 3 or 4 way valve or P/S piping and low temperature boiler protection.

nicholas bonham-carter

Steam to hot water conversion

You might do a search here for posts related to these conversions, and their many pitfalls. You would be better off making the steam work as well as it once did when first installed.

Principally, the increase in pressure by a factor of 20 times may give some leaks where they will do the most damage, and the reduction of temperature of the heating medium from 212 degrees down to 140 may mean the radiators will have to be much larger to do the job effectively.

In terms of reliability, I don't think that relying on a mechanical pump, can come close to a heating system with no moving parts!--NBC

Zman

Reverse indirect

I am concerned about short cycling with such a large single stage boiler. You could use an indirect, in reverse as a buffer/DHW tank. What are you hot water needs. Do have large tubs and high flow faucets? I will post more when time allows.Your plan with the TRV's is sound. There are definitely Wallies in your area.

Carl

Gordan

Hardly no moving parts! :-)

No parts moving at hundreds to thousands of RPM, certainly... fewer moving parts, yes. No powered parts, sure. But certainly there are moving parts (some of which have a reputation for finnickyness) that are key to safe and efficient operation of steam heating. It certainly is an elegant system.



One additional thing to mention with regard to converting steam rads to hot water is that not only do they operate at higher temperatures, but they get a goodly bit of their heat output from phase change (water vapor to liquid) whereby the latent heat of vaporization is released.

Tristan

steam to FHW conversion

@nicholas bonham-carter, thanks for your concerns about steam to FHW

conversions. My system was actually baseboard all around. I salvaged

steam radiators and converted them to FHW. 

Tristan

Short cycles and Tekmar 260

 @Zman and gennady, thanks for your advices. I know the boiler is overkill, but it was installed by the utility company under the previous owner of my house. There is a DHW tank, but on a different circulator. Do you mean that I should hook up, the returns of the rads on the tank to use it as buffering device? What else could be done to minimized short cycles firing,  without changing the boiler? What about the Tekmar control device, I wanted it because there is on this wall so many positive reviews of it. Apparently some people have successfully installed it on Burnham RV boiler, the same that I have. Or do you think is not necessary?

Zman

My concern

My concern is that by adding TRV's you are creating  micro zones. You could have radiators emitting only a few  thousand btu's powered by a boiler that only knows how to produce 100,00 +. It will short cycle like crazy.

The trv design you have is great

The tekmar is a great product

I don't know that model well enough to comment on the "near boiler" piping.

The short cycling can be resolved by a buffer tank. One way to do it is the to use an indirect water heater backwards. The upside is that you eliminate short cycling. The downside is that you loose the dhw storage that you may need to fill large tubs or get past high demand times.

Not all indirects can do this. The triangle tube smart has steel on the boiler side so would not work. Many others will.

You could always put in a boiler buddy or similar buffer tank.

Just a thought

Carl

gennady

buffer

If you will decouple boiler from the system via primary secondary piping or diverter valve, the high mass boiler becomes buffer tank itself.

Zman

Buffer

It looks like the boiler has some bipass piped internally. The instructions were not clear. Siggy did an article called "keeping the masses online" I will look for it when I get a chance. The boiler hold about 5 gallons calculating the Iron mass is the question.

Carl

gennady

Short cycling

If boiler holds 5 gal of water and it us warm outside and then water temperature to the house will be a 130 F. For sake of argument. Boiler differential is 20F . 180-160F. Then boiler holds 20x 5 x 8.33 x 60=49980 BTU hr. It means boiler will fire once an hour Max

Gordan

I think you're using the wrong formula

The question you're answering is "what boiler output (in BTU/hr) do I need to provide 5 gpm at 20 F rise."



It only takes 8.33 (BTU/gal x deg F) x 5 (gal) x 20 (deg F) = 833 BTU to raise the temperature of 5 gallons of water by 20 F.

gennady

Heat

ok

Tristan

More details

Thanks Zman, Gordan and gennady. I'm  hanging  on to the discussion, even if it starts to be a bit out of my reach!

Here are more details about my project. . The heatloss of my house is about 40000btu. The Burnham RV5

boiler is rated at 99,000btu! I have 8 radiators, the largest radiator is 9000btu @180F. I

also have DHW tank on a different circulator.  I call the MA rep for Boiler Buddy buffer tank, and it goes for more than $700. Any other cheaper tricks to get this short firing cycles under control? I understand that the

Burnham RV is condensation proof, and can handle low temp (55F) return water,

is that correct?

Gordan

Buffer sizing vs. DHW

The scenario you describe only offers 833 BTU of storage. In order for that buffer to only need to be replenished once an hour, you would need a heat loss of only 833 BTU/hr.

With a heat loss of 49980 BTU/hr, you'd need a lot of gallons to fire only once an hour over a 20 degree F differential. Using Heat Flo's buffer sizing formula:

V = t * (Qoutput - Qloss)/(dT * 500)

So, if we say that the boiler has a 90000 BTU/hr output and the heat loss is 50000 BTU/hr, and we want one firing per hour with a 20 F differential, then

V = 60 * (90000 - 50000)/(20 * 500) = 240 gal.www.heat-flo.com/pdfs/Buffer%20Tank%20Sizing%20Guide.pdf

Gordan

It's not condensation-proof...

It does have an internal bypass with variable speed injection, which prevents condensation, so it would not require you to install anything externally to prevent overly cold system return from reaching the boiler. You're good to go from that point of view. :-)



It's still vastly oversized for what you need... Nearly by a factor of two, and that's on the coldest day! As was already mentioned, you could use the indirect in reverse as a buffer, if it is built appropriately for that. What make and model of indirect do you have?

Tristan

Indirect water heater

Gordan, of the top of my head,  it's a Superstor Ultra Indirect SSU45 (45 gal). I'll confirm the model later this evening.

Thanks

Gordan

I don't think that would work as a reverse

The materials would be ok from the corrosion point of view, but the size and location of the coil doesn't really seem like it would allow much of a temperature rise. I'd be concerned.



You could get an electric tank and use it as a buffer. These will typically be limited to somewhat lower temperatures, though.

Harvey Ramer

I think this situation calls for an invention

to be made. Would it not be ideal to be able to run the low end water temp in the boiler on an outdoor reset and always allow the boiler to run up to 180 deg. The Odr on the boiler would always make sure you have hot enough water but in some sense act as a buffer by allowing the temp to go up to 180 every time. You would then use an I-series 4-way mixing valve with Odr and boiler protection instead of primary secondary piping. This would add additional buffering for the boiler and increase comfort.

gennady

buffer

ok

Zman

The article

Here is the Siggy article I was thinking of.



http://www.pmmag.com/Articles/Column/54b2e6286efc7010VgnVCM100000f932a8c0____ 



 Any idea what your boiler weighs?

Crunch

Blank

Carl,



This is a blank PM page, at least on my machine.



Crunch

Zman

Try

Here is another link

http://www.pmmag.com/Articles/Column/65b96bb047fc7010VgnVCM100000f932a8c0____

 If it doesn't work just search "managing masses" or "masses online" there are 2 good articles.

Carl

Crunch

Works

This one works!



Crunch

Tristan

ok

Tristan

ok

Tristan

Cheap electric water heater as buffer tank and boiler control

Thanks everyone. Does anyone has used cheap electric water heater as

buffer tank in a similar situation that I'm in? If the water heater as

rated range is 90-160F, will it be alright for 180F from boiler return?

Any recommendation on how to plumb it on the return line. Also, what

kind of boiler control with ODR would work well with Burnham RV5, Taco

SR504-1, and TRVs on all cast iron radiators?