Hydronic heating system antifreeze Q

[Waramanga]

Hi all,
I have a small boiler plant supplying hot water radiators. The boiler has to be outside but we get -10 sometimes warming up to +10 in the day say here. What are the pros and cons of using antifreeze? Is it a problem itself. Apparently some small packaged boilers just fire the boiler to take care of the freezing problem. What recommendations can you guy make? thank you for the help!

 

[GMcD]

Use a mixture of 20% to 25% inhibited propylene glycol for the system fill. It's not a high enough % of glycol to really affect the heat transfer of the terminals, so there is no design impact ("little" design impact for you gnit-pickers). I trust the piping from the boiler to the building, as well as all the heating piping in the building is thoroughly insulated?

Another option is to use some electric heat tracing on the outdoor piping, but what is not known is whether the boiler is in a heated enclosure? Or is the boiler itself sitting outside in the open air?

 

[Waramanga]

Thanks GMcD,
Yes the boiler itself is outside as is the expansion tank and pump. How about running the pump intermitantly to transfer a bit of heat from inside the building to stop freezing? I guess the expansion tank will still freeze though. Any thoughts?

 

[GMcD]

Cycling the boiler and pump as an anti-freeze method defies all energy efficiency criteria, and an exposed expansion tank will freeze unless the whole system is filled with a glycol mix. Why can't the boiler be placed in at least a cheap insulated shed? Why can't the pump and expansion tank be inside the building? I really don't like the description of this system, even if it's a temporary heating thing, it's just not right.

 

[ChrisConley]

Inhibited glycol has some advantages as well, in addition to freeze protection, it can replace a good chunk of a chemical treatment program.

I've never understood the outdoor boiler concept, unless it is a biomass boiler...

 

[Waramanga]

Well, I wish that the builders didnt know how many $/m2 the building was going to be able to be rented out for. that way they might be keen to hand over 5m2 for a plantroom and we could avoid the need for glycol and insulation on the pipes. lucky just to have them build a roof over the boilers head!!

 

[Compositepro]

There are some advantages to putting fired boilers and chemical plants outdoors. If you get a leak it is less likely to blow-up.

 

[ChasBean1]

Waramanga, for this climate you'd probably need at least a 30% glycol solution, resulting in some heat capacity reduction. Heat trace would require much attention to detail with dead legs, gauge lines, blowdown lines, expansion tank, additional electrical cost etc., all of which would probably outweigh efficiency losses from a glycol system.

 

[Waramanga]

Ok so how much space do you need for say a 50kw boiler if it was to go inside the building? Sure it depends on the exact boiler type but just a ball park figure for a comfortably sized room with ancillaries. 1m clearance all around the boiler and some wall space for zone valve etc?
cheers

 

[GMcD]

That's just a little guy - you can get small wall hung condensing boilers, along with the accessories (Pumps, expansion tank, air separator, chemical pot feeder, etc.) that should fit into a foot print of 5 feet x 5 feet (1.5M x 1.5M) or less depending on the brand. Cheaper conventional mid-efficiency boilers sit on the floor, and you can fit these into about the same size room depending on the brand and configuration. The local boiler suppliers can provide layout clearances (or internet source catalogues).

Don't forget the combustion and relief air inlet/outlets as per gas codes for an enclosed boiler room.

 

[Waramanga]

Thanks GMcD,
The wall hung option makes sense in this case because there are two zones that make sense, so i could use 2 x 25kw wall hung units, but.... the pumps that they have built in only deigned for a few meters of pipework in a domestic situation, how would one extend the range? use the boilers internal pump as a primary pump and then run a secondary pump off that loop?
Any ideas, comments, opinions?

 

[GMcD]

Waramanga asked: how would one extend the range? use the boilers internal pump as a primary pump and then run a secondary pump off that loop?

Yes, that's right. if the piping and terminal heating devices are low pressure drop type, then even the boilers' optional on-board circ pump could do it, but an add-on circ pump selected for the flow and head required for the heating system would be the right thing to do.