Best method of plumbing ZV for wood/oil switch

[kopeck]

So part of doing it your self is messing up. At least that's what I've been telling my self, it how you learn right?

When I plumbed in my Tarm Solo Innova I thought I had done everything, well it turns out I had forgot to put a zone valve in the line to my oil boiler that is suppose to prevent hot water from circulating back into it when I'm on wood/storage. I solved this by just shutting a ball valve by hand and manually turning off my oil boiler. It worked for the winter but there was no automatic backup which is a bit of a pain.

So I have a choice a the moment. The way the folks at Revision Heat like to setup their systems is both the wood and fossil fuel boilers dump heat into storage. Currently I have a Johnson Controls A419 on my storage that I can use to control the oil boiler. If the tank dips below a set temp the oil boiler kicks on and bring it back up.

The way my system is setup now is my Taco Zone Controller is what controls the operation of my oil boiler via the end switch. If there's a all for heat the switch closes and allows the boiler to fire if it's below temp. Pretty simple.

So here's my question. I could go to the Revision model which is supposedly more efficient since you are running the oil boiler for longer period vs. short on/off cycles. They also assume I have a DHW coil in the tank, which I don't have at the moment, I have an indirect hot water heater.

The other option would be to use a 3 way valve in place of the other ZV and install it where everything Tees in. When the temp of the tank it down the oil boiler would work the way it's setup now and just kicking on when the zone controller calls for heat. When the tank is up to temp the oil boiler would be shot off and water would flow from the wood boiler/storage. I would be more or less using the A419 as a switch between the end switch and the oil boiler (which is how I have it wired at the moment). Pretty much when oil boiler is needed the wood/storage side shut off.

I plan on burning wood during the heating season and oil when there's no call for heat, pretty much just for hot water. Am I really going to gain that much by keeping my 820 gallon tank hot all summer just to supply my DHW (via indirect hot water heater) or am I better of just letting my oil boiler take care of it on an as need basis?

Here's what my setup looks like (thanks to Revision Heat):

Thanks,

K

 

[hobbyheater]

I plan on burning wood during the heating season and oil when there's no call for heat, pretty much just for hot water. Am I really going to gain that much by keeping my 820 gallon tank hot all summer just to supply my DHW (via indirect hot water heater) or am I better of just letting my oil boiler take care of it on an as need basis?

If the oil boiler has to maintain its reservoir at stand-by temperature to produce DHW (via indirect hot water heater), it will be more economical to run using heat storage. Our storage is 1000 gallons unpressurized. Heating the storage with the oil boiler represented a savings of around 60% compared to running the oil boiler in stand by to produce DHW.
My preference is to run the wood boiler year round. That way you don't have any issues with the boiler sitting idle for an extended period of time.

 

[Bob Rohr]

So part of doing it your self is messing up. At least that's what I've been telling my self, it how you learn right?

When I plumbed in my Tarm Solo Innova I thought I had done everything, well it turns out I had forgot to put a zone valve in the line to my oil boiler that is suppose to prevent hot water from circulating back into it when I'm on wood/storage. I solved this by just shutting a ball valve by hand and manually turning off my oil boiler. It worked for the winter but there was no automatic backup which is a bit of a pain.

So I have a choice a the moment. The way the folks at Revision Heat like to setup their systems is both the wood and fossil fuel boilers dump heat into storage. Currently I have a Johnson Controls A419 on my storage that I can use to control the oil boiler. If the tank dips below a set temp the oil boiler kicks on and bring it back up.

The way my system is setup now is my Taco Zone Controller is what controls the operation of my oil boiler via the end switch. If there's a all for heat the switch closes and allows the boiler to fire if it's below temp. Pretty simple.

So here's my question. I could go to the Revision model which is supposedly more efficient since you are running the oil boiler for longer period vs. short on/off cycles. They also assume I have a DHW coil in the tank, which I don't have at the moment, I have an indirect hot water heater.

The other option would be to use a 3 way valve in place of the other ZV and install it where everything Tees in. When the temp of the tank it down the oil boiler would work the way it's setup now and just kicking on when the zone controller calls for heat. When the tank is up to temp the oil boiler would be shot off and water would flow from the wood boiler/storage. I would be more or less using the A419 as a switch between the end switch and the oil boiler (which is how I have it wired at the moment). Pretty much when oil boiler is needed the wood/storage side shut off.

I plan on burning wood during the heating season and oil when there's no call for heat, pretty much just for hot water. Am I really going to gain that much by keeping my 820 gallon tank hot all summer just to supply my DHW (via indirect hot water heater) or am I better of just letting my oil boiler take care of it on an as need basis?

Here's what my setup looks like (thanks to Revision Heat):

Thanks,

K

How and where is the indirect piped into the system? If it is piped and pumped properly the oil boiler should only fire when the indirect calls for heat. Really no need to maintain the boiler temperature as along as all the oil boiler output can go directly to the indirect.

Does the Tarm have the ability to heat the indirect also, without heating the large storage?

 

[kopeck]

How and where is the indirect piped into the system? If it is piped and pumped properly the oil boiler should only fire when the indirect calls for heat. Really no need to maintain the boiler temperature as along as all the oil boiler output can go directly to the indirect.

Does the Tarm have the ability to heat the indirect also, without heating the large storage?

Sorry, I should have made that more clear but my post as getting long as is.

The indirect is on it's own zone, so it can be heated by wood, oil or storage just like any heating zone in the system. The indirect is a Vaughn Top Performer (http://www.vaughncorp.com/html/tp.html), it has it's own thermostat and will maintain the water that's sitting in it at a set temperature, that is the boiler will fire even if there's no call for DHW.

I hope that makes sense...

K

 

[hobbyheater]

, that is the boiler will fire even if there's no call for DHW.

A hour meter was connected to the burner on the oil boiler. The burner would run 3 hours a day with no draw for DHW or house heat. With the boiler heating storage for just DHW, it would run for 3 hours every 5 to 10 days!

 

[kopeck]

Interesting. I guess I was wondering if it made sense trying to keep 800 gallons of water at say 130 to 140 deg or 30 gallons at 110.

I don't know the answer, that's why I asked. I know it would be better with a coil in the tank, the X factor is the indirect. I do know that the indirect will still give me decent hot water with the tank down to 120 or so deg.

K

 

[BoilerMan]

Interesting. I guess I was wondering if it made sense trying to keep 800 gallons of water at say 130 to 140 deg or 30 gallons at 110.

I don't know the answer, that's why I asked. I know it would be better with a coil in the tank, the X factor is the indirect. I do know that the indirect will still give me decent hot water with the tank down to 120 or so deg.

K

I would think your right about 800+ gallons at 140, seems like more oil would be consumed, than just fireing for DHW only no storage.

A hour meter was connected to the burner on the oil boiler. The burner would run 3 hours a day with no draw for DHW or house heat. With the boiler heating storage for just DHW, it would run for 3 hours every 5 to 10 days!

Although this contradicts this theory........ HH can you clarify some? What was the storage temp? Pressureized or atmospheric storage? Oil differential or cold start with aquastat on storage?

Seems like you should loose the indirect and get a coil for the DHW in the storage then the useable heat would be down to 115 or so.

TS

 

[kopeck]

Yeah, that's where I'm hung up. I know that the oil boiler is going to produce X BTUs when running but the indirect can only use so many of those BTUs so some are being wasted. I guess it's figuring out where the point of diminishing returns is.

K

 

[hobbyheater]

Although this contradicts this theory........ HH can you clarify some? What was the storage temp? Pressureized or atmospheric storage? Oil differential or cold start with aquastat on storage?

Seems like you should loose the indirect and get a coil for the DHW in the storage then the useable heat would be down to 115 or so.

TS

Storage is 1000 imperial gallons - very well insulated and is operated under static pressure with a open ended expansion tank on the floor above. There are two coils in the storage tank - one for DHW and the second to supply the zones at 5 to 7 PSI. The storage tank is a old steam boiler with its tubes removed (5/8" riveted plate steel) and sits on concrete saddles, putting the bottom of the tank 4' above the floor. No valving is needed to prevent hot water circulating back through the boiler when it is not running and creating stack loss. The oil boiler was controlled by an aquastat in the the storage tank and would start up when storage dropped 145 degrees and would turn off when the storage tank reached 180. This burn would usually last about 3 hours.
The oil boiler was a cast iron sectional weighing around 300 lbs and held a total of about 3 gallons. It had an internal coil for domestic hot water supply and would maintain a temperature of 170 to 180 degrees for this function. In the days of $0.35 a gallon for furnace oil, this boiler would really produce. BUT! An hour meter was connected to the burner of the boiler and with the boiler isolated so no domestic or house heat could be drawn from it and was run in standby mode for 72 hours and over the 3 days, it ran for more than 9 hours. Huge stack loss factor!
The oil boiler was then plumbed to storage and would run an average of 9 to 10 hours a week. In the summer, storage would last on an average of 5 days and occasionally as much as 10 days, when the only demand was DHW.
The oil boiler was connected to storage about 20 years ago but over time we used it less and less to the point our furnace oil was turning to jelly. Our back up is now electric, but this system runs independently from the wood system.
I have added a picture of the side of the storage tank and the concrete saddles it sits on.

 

[kopeck]

Your setup is similar to mine. I have 820 gallons of unpressurized storage with a coil that both heats and draws heat from my tank (as seen in the diagram above). I guess the other factor, one that's not 100% rational is that I've been dealing with a leaking tank (bad liner) all winter. I have a new liner and will install it soon but if for some reason I should have trouble again and have to drain the tank I'm with out heat since my oil boiler would be tied to the tank too. Like I said, if everything was working right it's a non-issue.

Maybe heaterman will weigh in here. If heating the storage tank was a clear cut winner I probably would feel better about it.

I know dropping a DHW coil in the storage tank would be idea but I can't afford that at the moment. At this point I need to go with what I have.

K

 

[maple1]

I'd seriously consider getting an electric hot water tank - if your oil boiler can stand being shut down for extended periods of time. I've kind of come to the conclusion that heating DHW with oil is a losing proposition.

 

[Bob Rohr]

I'd seriously consider getting an electric hot water tank - if your oil boiler can stand being shut down for extended periods of time. I've kind of come to the conclusion that heating DHW with oil is a losing proposition.

Good point. I think the first step is determining how much DHW you use per day. Then calculate what the cost to generate that with oil, electric, or heating all that storage.

If the electric rates are low, and you have enough power available even a tankless electric could be a good option. If your use is low, why bother storing any DHW?

When the wood is fired up for the heating season switch over.

 

[BoilerMan]

I'd seriously consider getting an electric hot water tank - if your oil boiler can stand being shut down for extended periods of time. I've kind of come to the conclusion that heating DHW with oil is a losing proposition.

Yes!! There was a thread on this about a month ago. As an electrician I've installed alot of them. The tankless option is only good if you have a 200amp service, you can tell if you check your main breaker. An electric tankless will save you money only if your DHW use is quite low, and infrequent. A cheap 'ol $300 4500 watt one from Lowes, HD, will serve well if you only use it in the summer, and drain it when not in use in the winter. An indirect costs close to nothing to run during the heating season, but is only around 40% efficient during the summer if used with oil w/o storage. Heating water directly with oil, Bock, Toyotomi etc. is the cheapest way to go, but equiptment and install costs are much higher. Electricity is expensive heat, but there are few looses from an insulated tank with no vent to draft heat out. I'm wondering about the heat pump electric water heaters, 220% efficient, and the ability to duct some of that cooled air into a bedroom..... still expensive install though.

TS

 

[hobbyheater]

I'd seriously consider getting an electric hot water tank

For DHW, all water feeds through the heat exchanger in the storage tank, then through a mixing valve set at 140 -145 degrees and then into a standard 40 gallon electric hot water tank. The elements in hot water tank are set to come on at 120.
Should storage drop below 120, there is a ready supply for domestic use.
The back up Monitron Electric Boiler is a demand type and is a manual switch over. Open one ball valve and close another and turn on its breakers and it's in operation.

 

[kopeck]

So, I guess what everyone is saying is that either way it's not going to be all that efficient...

An electric might be cheaper to run but I'm trying to spend a lot at the moment. If I was going to go that route I would want to get a heat pump...there goes the budget!

Thanks,

K

 

[BoilerMan]

So, I guess what everyone is saying is that either way it's not going to be all that efficient...

An electric might be cheaper to run but I'm trying to spend a lot at the moment. If I was going to go that route I would want to get a heat pump...there goes the budget!

Thanks,

K

A typical electric 40gal will work fine for your needs, they are $375@ Lowes. It's only going to be used for 4 months (remember we live in Maine), just be shore to isolate it with ball valves and drain during the heating season.

Oh, not that it needs mentioning, but turn it off before draining in the fall, and make shore it's completly full (air purged from T+P valve) before turning it on in the spring. You wouldn't believe how many prople burn the top element due to air in the tank.........

TS

 

[kopeck]

A typical electric 40gal will work fine for your needs, they are $375@ Lowes. It's only going to be used for 4 months (remember we live in Maine), just be shore to isolate it with ball valves and drain during the heating season.

Oh, not that it needs mentioning, but turn it off before draining in the fall, and make shore it's completly full (air purged from T+P valve) before turning it on in the spring. You wouldn't believe how many prople burn the top element due to air in the tank.........

TS

Come to think of it I have the unit that came out of my house. I can't remember how big it is, I'm thinking 30 gallons. The funny thing is it's also a Vaughn product (I just realized this). Had to special order the thing for my grandfather, it's stone lined. The first one that had lasted 30 years and was stone lined, why change.

http://www.vaughncorp.com/html/electric.html

I'll look it over, maybe it makes the most sense.

K

 

[heaterman]

I have to say the storage vs direct feed to the DHW tank depends a lot on how well the storage is insulated. I would want to know what the standby loss is on your tanks with no loads applied before i made a judgement on that.

Example: I had the opportunity to monitor a Garn2000 for 10 days while the homeowner was away. He fired it to 180 m/l and shut off the pumps letting his gas boiler do the work while he was gone. The Garn went from approx 180 to 105 over a period of close to 216 hours.
If we figure the Garn at its listed capacity of 1900 gallons that's 1900 x 8.33 x 75* or 1,187,025 btu's of heat loss at an average rate of about 5,400 btu's per hour. (The Garn is in an insulated but totally unheated outdoor structure.) It wears one of my Garn "sweater" insulation kits and that is all. Basically R-16 all the way around it.

If i were you I would try to get a handle on the heat loss of your storage by doing the same thing. Fire it up to temp and let it sit with no loads on it and check your temp drop over a week time period.

As I recall, you and I had corresponded about a 3-way valve that would divert from wood to oil whenever the oil boiler came on?

 

[kopeck]

Here's my tank:

http://www.americansolartechnics.com/heatbank820.html

So it's R 31 Walls and R 24 top. I don't know what the real world heat loss is though. I would test it but I have the tank drained to replace a leaking liner so until that happens I'm stuck.

Yes, it was me. Pretty much it's either a 3 way that keeps the oil boiler directly feeding the manifold (and there for the indirect) or a normal two way and my oil boiler feeding the storage tank.

K

 

[kopeck]

So this is what I've learned.

There is no really efficient way to heat DHW with oil. I might gain some efficiency by loading my storage tank with the oil boiler but it's still not great since then I have to deal with heat loss and since my DHW use is all over the place in the summer I'm willing to bet it's not going to be quite a big of a gain as I might like.

So here's my plan. I'm going to go with a 3-Way valve that will more or less separate the oil boiler from the wood/storage. What I like about this setup is if something happens with the wood boiler or the storage tank I can eliminate that whole side of things and fall back on oil by just closing two ball valves. This is for the paranoid side of me.

Ideally I think the best next step would be to eliminate the indirect completely and go in another direction. I'm thinking a DHW coil in my storage tank that would feed a heat pump hot water heater and maybe some solar mixed is as well. That for the future though. I do have a plain old electric hot water heater that I could use in the mean time. I'll see if I have the time to plumb it in and at least play some.

That doesn't seem like to outlandish of a plan, right?

K

 

[Bob Rohr]

So this is what I've learned.

There is no really efficient way to heat DHW with oil. I might gain some efficiency by loading my storage tank with the oil boiler but it's still not great since then I have to deal with heat loss and since my DHW use is all over the place in the summer I'm willing to bet it's not going to be quite a big of a gain as I might like.

So here's my plan. I'm going to go with a 3-Way valve that will more or less separate the oil boiler from the wood/storage. What I like about this setup is if something happens with the wood boiler or the storage tank I can eliminate that whole side of things and fall back on oil by just closing two ball valves. This is for the paranoid side of me.

Ideally I think the best next step would be to eliminate the indirect completely and go in another direction. I'm thinking a DHW coil in my storage tank that would feed a heat pump hot water heater and maybe some solar mixed is as well. That for the future though. I do have a plain old electric hot water heater that I could use in the mean time. I'll see if I have the time to plumb it in and at least play some.

That doesn't seem like to outlandish of a plan, right?

K

I agree the oil boiler should never heat the storage tank, too much loss in moving the energy back and forth and standby loss from a large tank.

But that does make DHW more of an issue, if you plan on a coil in your storage for DHW. All things can be accomplished but the more variables or options the more components and control wiring is required. And more things to break!

Ideally you would define your DHW load first, is it 20 gallons a day or 80 or more? Then it is easier to design the best solution.

The average DHW consumption has been suggested as 20 gallons per person per day. I feel, for most that is high. Some suggest 20 gallons per day for the first two occupants and 10 gallons per day for additional. The very best way is to put an inexpensive water meter on your DHW supply and see exactly what your household uses. DHW consumption varies a lot from family to family. But you would be surprised how little you can get by with if you are so inclined.

The tankless concept if my current favorite. It could be tankless via a coil in a storage, a tankless LP or electric fired stand alone, or use a plate HX and generate the DHW as demanded.

Solar can make a big difference in your plan. You should be able to easily get a 50% solar fraction most any locations in the US, with a few collectors and 80 gallons of storage. Wood fired could provide most of the heating season DHW load. So then all you need to cover is the non sunny days in the summer months. I can go 3 days on a 120 gallon solar tank without full sun. Now that remaining load looks do-able with an electric tank or small tankless style heater, remembering the solar will always pre-heat even on overcast days.

Another approach is to build a DHW system around components you have or parts you could buy and assemble yourself. So economics and DHW loads need to be balanced against one another. There really is no simple one answer DHW system, the fun is in building the system that meets all your criteria.