flow rates, heat loads and more

[rotaxman]

I have a question that relates to a topic here https://www.hearth.com/talk/threads/40483/

I've been lurking around here for quite some time and have read as much as I possibly can but still have a couple unanswered questions. My head is still spinning but here it goes anyway.
I have a similar situation as the thread above but my maximum loop is 250' of 1/2" and I have 6 of them @ 8" apart. 900 square feet
I'm wondering what the btu output would be. Is there a chart available for this?
I have my heat load calcs at home but I think the basement was 15000 btu/hr, According to what I just read in the link above, the .6 gal/min will be more heat than I need, should I control this with less flow or lower water temp?
I will be controling this zone and the zone on the main floor with pumps and that's something that I've been agonizing over, control with pumps or valves but anyway.

Another question I have, what is the advantage of having a circulator pump just for the OWB and other pumps just for the zone's? as opposed to just having zone pumps do all the work? If the boiler circ is running, will the zone pumps stop the flow of water to the zones when they are not running. My boiler will be about 50 feet away and temperatures can get quite frosty, minus 30 C can last a week is that makes any difference.

oh, and one more question, when doing the heat load for a main floor that has cathedral ceilings and 80% glass on the south side, how do you take into account the slolar heat gain? or is this offset by the heat loss at night and cloudy days?

oh, one more question, how do I size my expansion tank? I have 2 zones with 6 loops in each for a total of 3000' of 1/2" pex. 200 gallons in the boiler and 40 in the electric hot water tank which will be my back-up.

Thanks in advance for any help. This is a great forum, I've learned a boat load since I started reading. When I started this project I thought I'd just get an OWB, a pump and some pex and a way I would go but the more I read the more I want to maximize the efficiency but then it becomes a question of money as well. Fun project just the same.

 

[Nofossil]

Welcome to the forum. It would help a lot if you have any way to draw up a diagram and post it. Too many questions.....

Do you have a heat exchanger between the boiler and the house? You mention OWB - what is the boiler in this case? As far as I know, OWBs are not typically pressurized and don't require expansion tanks.

Heat load calcs are worst case - they tell you your heat loss with no solar gain. Depending on your situation, your net heat loss on a sunny day could be 0.


I'd be surprised if an electric hot water tank could provide enough heat to serve as a backup. Of course, I've been surprised before.

 

[rotaxman]

It was my original plan to post the diagram but didn't do it. I'll scan it at work tomorrow and put it up here so that you can see what I'm doing or trying to do.
well that answers my question about the expansion tank. Although the system is not pressurized, I thought it was necessary anyway. If I don't fire up the outdoor boiler and use just my hotwater tank, which I would like to do at this time of year, I would need the expansion tank wouldn't I?
I will be putting a heat exchanger, but maybe not this year, I'll include it in the drawing.
stay tuned.
thank you for the welcome

 

[sgschwend]

I believe it is wise to have a circulator pump for the boiler so that boiler controls can manage the water temperature.

If you take a look at the simplified diagram in this section a second pump is used to move the water to the loads. Thermostatically controlled zone valves both send a run signal to the pump that service the load and open the zone valve.

With this design you have two systems connected together. One make hot water, the other draws hot water and returns cold water. Much simpler to understand and take care of.

 

[rotaxman]

I know what you mean about the zone valves and probably more efficient but I'm wondering about cost. I would like to price out the difference but not sure what exactly I'm shopping for and the two dealers I know of here in the Ottawa area either clam up when they find out that I'm not a contractor or just refuse to help me at all. Do you have suggestions for zone valves that I can shop for?

Did I understand correctly that in a zone, you calculate the head for the longest loop and that's it for the whole zone?
If that's the case, the two zones would be approx. 8' of head including elbows and I can get by with one 15-58 for the whole system, if I use zone valves.

I just tried to upload a pdf but no go so..........

I will try to explain my intentions for this system. oh, and btw, I answered my own question about having a primary and secondary system, The heat X requires it.

The primary loop would enter the house and go into the electric hot water tank and then to the heat X then back to the boiler. Second system has either zone valves or zone pumps and I presume that I will need check valves where each zone returns to the primary system.
I don't know what's available for controlers but I would like the heat x to be closed when a zone is calling, the heat x is only to heat the water before it enters the DHW tank. There's just my wife and I so hot water is not in large demand.

I think I have enough questions for now. The possibilities seem endless, the more I learn, the more elaborate I would like the system to be.

 

[sgschwend]

Taco and probably others have valves in the $80-90 range depending on the size you purchase. I would use the Internet to make these purchases if you locals are not interested in making a sale.

You may find this information helpful:

(broken link removed to http://www.blueridgecompany.com/documents/102-111new.pdf)

 

[rotaxman]

thanks for reminding me about the sticky threads, "primary secondary" I had read it a couple months ago but now that I understand what I'm reading, it's answering some of my questions. I will make another attempt at a drawing and repost my questions. Stay tuned and thanks.

 

[rotaxman]

I have a new drawing and as you can see I've decided to go with zone valves and just one pump for the entire system. I would like to provide a few more details. This is a brand new home, first winter. It's a log home and except for the log work, I built it from the ground up so I know that it's as air tight as a log home can be. The walls are considered to be better than R20, the logs are white pine and are between 18 and 26 inches in diameter. I used R20 in the heat load calc but my walls hold heat in them instead of being a cold barrier. The heat load for the whole house is 46000 BTU's and is difficult to seperate by floors because of the cathedral ceiling, all glass gable in the great room and the open loft(no walls) except for the upstairs bathroom.
Please provide critisism on my design. Nofossil, I used your design and symbols and have a few questions, but later.
I have a few questions on my design.
The electric hot water tank is for spring and fall or if I'm late getting home from a weekend of snowmobiling and the water temp gets too low. I would only want it to supply one zone, main floor so my question is, should I use a small tank (5-10 gal.)that would recover quickly or a large tank with more capacity(40-60 gal)
Nofossil, you have an air seperator, why is that needed?
I would like to know what my heat output will be, I saw a couple formulas in threads here but none of the ones I saw take into account the amount of space you're covering with your loops. and the reason I ask is that I'm worried that on the cold cold winter nights like -30, it may be drafty on my south wall that is 80% glass. I have a wood fired fireplace that will overcome this but I want to be able to heat solely with the radiant if I can. The great room floor is pine, will have staple up pex under it and can be at 6" apart if needed. The rest of my floors are tile with 1/2" cement board as the subfloor.

Zone 1 is 1/2" pex and 8" apart covering 900 square feet, longest loop at 250'
Zone 2 will be at least that of zone 1 maybe at 6" spacing in front of all the glass
Zone 3 is still under construction and I haven't decided if I will put a rad or more pex, just in the bathroom. It's gonna be hot up there until I get the air exchanger hooked up.
There's also the heat exchanger for the domestic hot water, this will be home made, maybe this winter sometime.
I will push all the water with a 15-58 for now, we'll see what the heatX does to the flow resistance.

I think I covered everything for now. I hope this picture uploads.

TYIA

 

[rotaxman]

crude drawing but I think it works

 

[Nofossil]

Thanks for the drawing - it helps. Nice first draft, but I have a few initial comments. I expect others will chime in as well.

To answer your first question - all hydronic systems require an air separator. Otherwise, bubbles accumulate and disrupt flow. There are a few books and resources out there that cover the basics of hydronic system design. The bible is John Siegenthaler's "Modern Hydronic Heating". Pricey and heavy going, but probably a good investment of money and time.

A DHW tank is way too small to provide any meaningful heat storage. An electric hot water tank plumbed as you've shown can provide around 20,000 BTU/hr if the electric elements are powered. That's less than half your calculated heat load. That may be enough for your needs, or you may want to look at a water heater with higher output.

The circulator won't work in the location shown - with the recirc valve open, it will flow backwards up the recirc line and bypass the boiler. One solution would be to move it to the left of the recirc tee.

Your wood boiler will likely put out water that's way too hot for radiant coils. It would be well worth your time and money to get Siegenthaler's book, or find a local radiant heat expert. One solution might be to move the circ up to the right side of the hot water tank and add a mixing valve just upstream of it so that zone return water is mixed with boiler water to give you the right temperature for your radiant zones.

Lastly, a sidearm DHW heater is not going to provide thrilling performance at the lower temperatures that radiant coils use. You'll want to plumb that over on the hot side. Most folks just run hot boiler water through the sidearm all the time, and add a mixing valve on the DHW outlet to prevent scalding. Sidearms have a very low recovery (heat transfer) rate, so waiting until your DHW is cool to start flow through the sidearm is not a recipe for domestic tranquility.

Keep in mind that advice offered here is just advice. No one here knows your local codes, insurance company requirements, or anything else. Heck, I don't even know anything about plumbing. Some insurance companies require 'adequate' backup heat sources in cases where the primary heat comes from biofuels.

 

[rotaxman]

Thanks for the comments, just what I was looking for.
I'll look for the book, try and find it for less than $100
any other books you would suggest?

I guess if 40-60 gal is too small for storage, I'll get a small water heater that can handle 20K btu, the total heat load at this time of year in my area is less than 20K, not enough to fire up a boiler.

The reason I had the circ there was to be able to run the sytem without the boiler, one zone valve would close off the boiler and the other one would close off the whater heater loop. I'll install a mixing valve where the bypass zone valve is and that will serve both pruposes.
The reason I had the pump on the cold side was for that reason, because it's colder but I could move, that's for sure.

I think I was confusing the air seperator and the expansion tank, I'll add the seperator.

Good plan for the heating coil, I wasn't sure what to expect, it will be home made.

My goal is to get up and running and make improvements. I see now that I will want a good controler, something I haven't shopped for yet. I may start with something simple but will want something more elaborate, I read something here about the Tekmar 157, is this a PLC? do you know if it or others can be plugged into a laptop for programming?

New drawing coming up

 

[Nofossil]

My goal is to get up and running and make improvements. I see now that I will want a good controler, something I haven't shopped for yet. I may start with something simple but will want something more elaborate, I read something here about the Tekmar 157, is this a PLC? do you know if it or others can be plugged into a laptop for programming?

Sorry - I don't know much about controllers ;-)

Seriously, others have first hand experience with te Tekmar and other controllers. My experience is more limited.

 

[Gooserider]

Thanks for the comments, just what I was looking for.
I'll look for the book, try and find it for less than $100
any other books you would suggest?

I guess if 40-60 gal is too small for storage, I'll get a small water heater that can handle 20K btu, the total heat load at this time of year in my area is less than 20K, not enough to fire up a boiler.

The reason I had the circ there was to be able to run the sytem without the boiler, one zone valve would close off the boiler and the other one would close off the whater heater loop. I'll install a mixing valve where the bypass zone valve is and that will serve both pruposes.
The reason I had the pump on the cold side was for that reason, because it's colder but I could move, that's for sure.

I think I was confusing the air seperator and the expansion tank, I'll add the seperator.

Good plan for the heating coil, I wasn't sure what to expect, it will be home made.

My goal is to get up and running and make improvements. I see now that I will want a good controler, something I haven't shopped for yet. I may start with something simple but will want something more elaborate, I read something here about the Tekmar 157, is this a PLC? do you know if it or others can be plugged into a laptop for programming?

New drawing coming up

For books, I've seen several people reccomend some of the books by Dan Hollohan (sp?) the guy that runs HeatingHelp.com and "TheWall"

For storage NF is quite right, 40-60 gallons is WAY to small... Gassifiers benefit greatly from having storage, but it has to be properly sized, which usually works out to around 1,000 gallons or so... You need to have lots of storage to absorb the heat produced by the boiler that is greater than the house load at any given instant, and let you heat the house from storage at a later time when the boiler isn't running. Think of it as a giant thermal "flywheel" in effect. This allows your boiler to burn flat out for an entire fuel load, which is it's cleanest and most efficient mode. Oncce the boiler has burned it's load of wood and the storage is charged, you then let the fire burn out, and heat off the storage until it's temperature drops to the point where you need to build another fire to charge it back up again. This might be just a few hours in the coldest weather, to several days in warm weather.

One big item that is currently missing from your diagram is an expansion tank - vital for safety reasons, and also provides the pressure reference point for the rest of the system - it should always be placed so that your pumps will "pump away" from the expansion tank if at all possible. (This is also where you will usually see your system filling hardware)

Gooserider

 

[rotaxman]

Been doing lots more reading here once again, so much knowledge here, enough for a book, which I have started, a binder with info. I ordered the book almost 2 weeks ago, must be held up at customs, none available in Canada.
The pump was moved to the hot side but I have to keep it in the loop where I can use the electric boiler without the OWB. BTW, I will be getting an electric boiler instead of the water heater. Is there anything else I need to consider now that I decided to go with the electric boiler? I presume that I would need a zone valve that would bypass the new boiler when using only the OWB? or is it not that easy?
I haven't been able to find any information on sizing the expansion tank and air separator, any ideas?

The zone for the main level will have a header. This zone will carry .6 gpm in 1/2" pex in each of 6 loops for 3.6 gpm total. This zone is capable of 36K BTU/hr with those figures and the load is 21K. from what I have read, a 3/4" header is sufficient? Yes?
I also read that a zone that has a header, should have it's own circ.......any truth to that statement?

nofossil, you once mentioned in this forum somewhere that adding HX to a pressurized system is not as easy as a system that is not pressurized, what would the reason be for that?

In regards to my heat load question earlier, about all my south side glass. I was able to find a calculator that counts your solar heat gain, taking into account your glass type and coordinates on this earth. September and March are the two best months, providing approx. 100BTU/day per square foot of glass for me.....if the sun shines and those damn maple, beech and oak leaves will fall off soon.

 

[Nofossil]

nofossil, you once mentioned in this forum somewhere that adding HX to a pressurized system is not as easy as a system that is not pressurized, what would the reason be for that?

In a pressurized storage system, heat exchangers pretty much need to be external to the storage. That means that they require a circulator on each side of the hx.

In comparison, an unpressurized storage system typically is a tank with an open top. Heat exchangers can be immersed in the storage tank. For instance, I have a domestic hot water preheat coil and a solar panel hx coil in my storage tank.

 

[rotaxman]

your pic explains a couple questions I had about your drawing in the "sticky"

Got my book (Dan Holohan) last night......exciting, more knowledge.

started to read it at lunch today, I couldn't wipe the grin off my face after the first couple pages.
now I want to try and grow a cucumber in a jar
This is going to be a great read

Be back when I can answer a couple of my own questions