Questions about a multihome metered system----first post

[churchillrow]

Hi,
First post from a long time lurker. I've got a long series of questions here about a proposed multi-home heating system. I've tried to read as much as I could on the forums and elsewhere before posting so I'm hoping not too many questions will be of the completely obvious variety but I won't make any promises.

First a short description of the context for this half formed plan of mine: A communal farm in northern Nova Scotia with seriously cold and long winters (trees are just budding out now.) Lots of hard wood available 70-80$ / chord in eight foot lengths. We want to heat

1. an old farm house with an existing system of cast radiators which are unused at the moment (we have been burning 10 chords per year in a large pacific energy and heating only half the house. (An energy assessment we had done pegged annual energy use for space heating and dhw at 270 million btu.)

2. A semi tight 900 sq. ft. bungalow and its unattached but insulated garage. (Based on present oil use space heating and dhw require about 80 million btu.)

3. A starting green house in the shoulder seasons

4. A proposed 1200 sq. foot straw-bale house

5. Perhaps some shop space etc.

The farm house and bungalow are 250 ft apart with a barn which seems appropriate for the boiler room standing roughly in the middle of the two. We would like the system to operate as a mini utility with the capability to meter the energy usage of each end user. I also have an interest in being able to plot system data in a similar way to nofossil as a means to being able to optimize the system performance and just for nerdy fun (although I must admit to being less competent nerd than I'd like).

I've tried to organize the following questions in a rational manner so if that if this post seems absurdly long you fire masters out there can bite off a chunk of your liking.

1. Boiler Sizing
I think I have a handle on the method of calculating peak load using degree days thanks to a post. Once I've got this number is there anything I should know` specific to wood boilers

a. what about twinning two smaller boilers for more efficient burns in shoulder seasons and for a more robust system?

2. Heat loss through piping
One of the major disadvantages I can think of for a multi-house system. Things I think I'd need to know to make calculations would be
a. Pipe diameter needed to service a house
b. normal flow rates

So far the best product i can find is pex flex which is distributed by Urecon in North America. Any other good options people know of? This stuff is very expensive (11$ per foot) and would make up a substantial part of the cost of our system offsetting a healthy chunk of the savings we'd get from buying one larger boiler.

c. I'm also curious about a means to purge stranded hot water from the end of a pumping cycle. Is this practical and or necessary?

3. Storage
I know there is a lot in the forum already about storage design and construction and I haven't read it yet so I skip asking about that.

a. What are the possible advantages / disadvantages to having the storage in close proximity to the boiler or distributed at each end user?

b. Is there an ideal ratio between peak demand and storage size or storage size and something else that I should know about?

4. Controller
A "homebrew controller" a la nofossil seems sadly out of reach for my level of technical expertise. Other options I have come across include a standard plc, a tekmar type controller, some more analog system which I don't have the vocabulary to express or whatever comes with the boiler. Are there other options? Considering the following desires which would be best?
a. prioritize radiator heated zones and dhw over radiant areas
b. prioritize certain users over others at peak demand if there is insufficient heating capacity
c. Some sort of alarm indicating a firing is required
d. minimize the number of "pumping cycles" between boiler and users.
e. enable eventual incorporation of solar hot water

5. Eco vs Garn type
I have seen both vouched for on this forum as quality products. Any opinions for this particular application?

6. Professional Help
I'd like to do as much as possible of the system design and construction. (with the help of the fine minds on this forum of course). On the other hand i don't want to do anything dangerous or needlessly wasteful of time or money. Here are some categories I came up with yeah or nay to DIY would be much appreciated. I have done a fair amount of plumbing and wiring around the farm but nothing close to this scale.

a. plumbing diagram, system design
b. installation of boiler
c. installation of storage
d. integration of controller
e. design of ladder logic if using a plc (i have a little bit of programming experience)
f. installation of zones and heat sources in house
f. others??????

7. Here are some advantages/disadvantages to multi-house system i have come up with. Any additions or subtractions to this list or or opinions as to wether the basic idea holds water would be much appreciated.

Adv
a. larger boiler cheaper per btu
b. reduces need for back up heat/ other will be stoking some of the time
c. presuming some surplus capacity makes heating new structures simple
d. enables those who aren't normally able to use wood heat like the elderly or disabled (considerations for future projects of the farm)
e. one controller


Dis
a. insulated piping is expensive (pex flex 11$/foot)
b. increased complexity
c. heat loss to ground
d.

Thanks for reading what feels like a long winded and demanding post. In our part of the world wood just makes a lot of sense and who can complain about lots of DHW (certainly not the wife). With heating oil prices headed the direction they are Biomass energy seems like the way of the future and I'd like to think of this project as a pilot for mini district energy systems. Imagine a boiler a boiler a the center of every block
Augie

 

[ugenetoo]

i cant really give you any answers(not nerdy enough??), but i do know that using two smaller boilers in order to achieve effeciency does work rather well. i had an old victorian home in northern maine with about the same weather extremes and used two older style 100k btu tarms to heat with. 75% of the time, only one was used, but when it dropped below 0 degrees farenheit, the second one was cranked up.
i also have tossed around the idea of metering heat from a large boiler/storage system, so ill be watching this thread!

 

[churchillrow]

The metering is something I didn't really get into in the post but I found some flow/temperature meters which i think will integrate the two numbers and give net energy use.
http://www.rshydro.co.uk/Heat-Meters-c-329.html

or even better and distributed in north america

(broken link removed to http://www.kamstrup.com/2431/MULTICAL%20401)

 

[hkazemi]

The farm house and bungalow are 250 ft apart with a barn which seems appropriate for the boiler room standing roughly in the middle of the two. We would like the system to operate as a mini utility with the capability to meter the energy usage of each end user. I also have an interest in being able to plot system data in a similar way to nofossil as a means to being able to optimize the system performance and just for nerdy fun (although I must admit to being less competent nerd than I'd like).

Where is the barn? Are you talking about building a new boiler room/shed, or about putting the boiler in the barn? If you're building a new structure, consider taking a look at Gary Reysa's Solar Shed project page (http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm ) and added solar collectors on the south facing side. Also plan for large scale storage, possibly using an insulated wet sand 'basement' under the shed, with one description being here:
http://listserv.repp.org/pipermail/greenbuilding_listserv.repp.org/2008-January/005891.html

1. Boiler Sizing
I think I have a handle on the method of calculating peak load using degree days thanks to a post. Once I've got this number is there anything I should know` specific to wood boilers

a. what about twinning two smaller boilers for more efficient burns in shoulder seasons and for a more robust system?

2 boilers would give you redundancy, but I think you might also able to use evac tube (see Sunmaxx Solar) or large flat plate solar to cover much of the shoulder season times.

2. Heat loss through piping
One of the major disadvantages I can think of for a multi-house system.
So far the best product i can find is pex flex which is distributed by Urecon in North America. Any other good options people know of? This stuff is very expensive (11$ per foot) and would make up a substantial part of the cost of our system offsetting a healthy chunk of the savings we'd get from buying one larger boiler.

Also look at http://www.insulseal.com/ and http://www.flexsulseal.com/ . They're similar to some of the Urecon products. Insulseal is rigid insulated PVC pipe that you'd run PAP or Pex through afterwards, Flexulseal has the lines built in. I prefer the 'conduit' style of Insulseal where the lines can be changed afterwards. Try to have them sloped to a drainage area in case a leak develops somewhere. You want good insulated pipe from the boiler/storage area to the homes so you don't end up losing huge amounts of heat to the ground melting snow.

c. I'm also curious about a means to purge stranded hot water from the end of a pumping cycle. Is this practical and or necessary?

Why? Are you trying to get the most energy out of the hot water, or are you concerned about stagnating water, or something else?

3. Storage
I know there is a lot in the forum already about storage design and construction and I haven't read it yet so I skip asking about that.

a. What are the possible advantages / disadvantages to having the storage in close proximity to the boiler or distributed at each end user?

You're choosing between a big central storage or distributed storage. If you go distributed, you'll have an easier time separating the systems if you need to in the future. If you go central, you may see cost savings from better economies of scale on large thermal storage and insulation, and you won't need to consume additional space at each end. Storage at the ends has the benefit (during the winter) that heat leakage goes to heat the home rather than a boiler or barn.

b. Is there an ideal ratio between peak demand and storage size or storage size and something else that I should know about?

Storage capacity will help determine how often you'll need to run your boiler and to some extent how large of a boiler you'll need. It's the same old argument of sizing for the median load vs. the peak load. Traditional tank style water heaters are sized for the median load while tankless water heaters need to be sized for peak loads. If you have solar thermal collectors, (very) large storage is even more valuable because you may even be able to seasonal thermal storage. If it were me, I would make the storage as large as practically possible, and choose a smaller boiler that can run at 100% for long periods. I think it is easier to add additional heat generating capacity afterwards than additional large scale storage.

4. Controller
A "homebrew controller" a la nofossil seems sadly out of reach for my level of technical expertise. Other options I have come across include a standard plc, a tekmar type controller, some more analog system which I don't have the vocabulary to express or whatever comes with the boiler. Are there other options? Considering the following desires which would be best?
a. prioritize radiator heated zones and dhw over radiant areas
b. prioritize certain users over others at peak demand if there is insufficient heating capacity
c. Some sort of alarm indicating a firing is required
d. minimize the number of "pumping cycles" between boiler and users.
e. enable eventual incorporation of solar hot water

These monitoring and control tools may be relevant to you:
http://www.ourcoolhouse.com/scada.htm
(broken link removed to http://www.ourcoolhouse.com/WEL/)
http://www.welserver.com/index.htm

Along with these:
http://diy-zoning.sourceforge.net/
http://haywire.sourceforge.net/
http://servomaster.sourceforge.net/

This meter is a way to measure the amount of energy each home/building is using:
http://www.thermomax.com/BTU_Meter.htm
it measures flow rates and the temperature difference between the supply and return lines to calculate how much energy has been moved. Independent sensors fed into a programmable controller or computer could be used to do the same.

System design note: I suggest trying to zone with valves, not pumps, to minimize the amount of continuous electric power needed to make the system work. A lot of pumps running continously can add up the KWHs. Low power DC pumps are available under the "El-SID" (i.e. static-impeller driven) label from Ivan Labs. See http://www.solarhaven.org/Hydronic.htm and http://shop.solardirect.com/product_info.php?products_id=363