What does right look like?

Brad White_9

As we have suspected, your boiler to heat loss ratio is getting wider!

Yes, the Primary-Secondary Made Easy is a worthwhile book especially if you want to understand the process and means behind it. Decoupling is another term for Primary-Secondary or rahter Primary/Secondary is a sub-set of decoupling.

There are several ways to do it:

4-way mixing valve (my personal favorite)
3-way mixing valve
P/S with injection pumping to the radiation loop
P/S with control valve injection to the radiation loop

Key is having a means to change the temperature in the secondary (radiation) loop by bleeding in more boiler-side HW and returning it to the boiler accordingly. The means is either a valve or a pump in the above examples. There are other ways also, but these are what come to mind.

Tekmar among other resources have diagrams and strategies (and the hardware to support them). John Siegenthaler (Siggy to his many friends) also has a book called Modern Hydronic Heating (2nd. Edition) which is a wealth of infirmation between two covers in my opinion.

ralman

What does right look like?

Please describe normal boiler operation. I have an oil fired peerless boiler 121,000 BTU gross output, Domestic hot water coil, 1 1/4 inch monoflo tee sytem, 185 feet of base ray CI baseboard. My aquastat setting are 180 high, 150 low, 15 differential. Normally, at 30 degree outside temperature, a call for heat will fire the boiler and circulator for 4-6 minutes. Even on the coldest days my boiler never reaches high limit. Normally within 5 minutes of shutting down from a heat call, the boiler comes back on, but not the circulator, because the water temperature fell below the low limit. Is this the way it is supposed to work?

Brad White_23

Need to know

what your caclulated heat loss is. If it seems to short cycle it may be a function of a mis-match between actual heat loss and boiler output.

In a high mass system like yours (CI Baseboard- you are blessed), my gut says it should coast better and longer between cycles.

The amount of CI BB you have at about 550 BTU/LF would emit about 102,000 BTUH on the coldest day with the hottest water so you are about 20 percent over-sized on the coldest day, more so on milder days. This is not to say that your heat loss might not be less. It probably is lower so the disparity is greater.

Part of the issue may be with regards to the "bang-bang" (on-off) control method of single-stage firing. A way around this is to de-couple the radiation loop from the boiler loop and bleed-in hot boiler water into the radiation loop to maintain re-set scheduled HW supply temperature there. This way your boiler fires to a pre-set limit (usually parallel to and 10 or so degrees above your radiation loop temperature requirements). Protects the boiler from too-cool return water and tailors output to your needs.

Again, though, without knowing the heat loss of the house, this is all conjecture.

Another thought: You have domestic HW off the boiler too. Might this also cause the burner to run and not the heating circulator? I would think so and suggest that you see if that is the case.


Brad

Rodney Summers

Too bad

you didn't get an indirect tank. You still need to keep the boiler hot for DHW, but it seems oversized for heating. You may want your boiler contractor to check if the boiler is over fired. You might get away with a smaller nozzle to get the burn times to run longer. I would also try lowering the low limit to 140°, 20° diff and probably a 170° high limit. See if you're still happy when you use DHW and the heat is calling at the same time. You have to still expect that you need the higher limit on design days when temps drop to the teens or less.

ralman

heat loss

My calculated heat loss for indoor temp of 80 degrees and outside temp of 15 degrees using slant fin program available from this website is 57,500 BTU's per hour. I am averaging 6 gallons of oil per day, which puts my heat loss average at 26,250 BTU's per hour. My thermostat is set just below 70 degrees and I have a seperate digital thermometer next to it that indicates 73 degrees room temp. I have tried different thermostat settings but this is where the home is most comfortable.

Brad White_9

80 degrees indoor??

And I thought "Some Like It Hot" was only a movie...

The gallons per day oil use and averaging that will only take you so far but for discussion it is fine.

You can see either way that you are seriously over-fired by almost a factor of two, even at 80F indoor temperatures. Is this a swimming pool or are there health concerns? Curious but maybe none of my business.

Good news is, your radiation is right up there, about double what you would need if your numbers are correct. Downsizing the nozzle will only get you so far, but you may want to consider decoupling the boiler from the radiation (many ways to do this) and allow yourself some deep curve reset in the process. You have the radiation, now you have to tame the relationship between the boiler and the radiation.

ralman

Decoupling

I have been playing around with different variables in the program to see how it effects the BTU loss outcome. I can change the 80 degree design temp in the program, I was just using that number to see what difference it made, 70 degree indoor temp brings heat loss to 52,258 BTU's. I purchased the pumping away book from this site and was considering purchasing the primary secondary piping made easy. Is this primary secondary piping what you mean by decoupling? Are there any good references to decoupling that I can get?