Definition of Serial vs. Parallel Piping Setup

[Eric Johnson]

This came up in another thread. Anybody want to take a whack at it? I'm looking for a clear, simple definition.

 

[steam man]

This came up in another thread. Anybody want to take a whack at it? I'm looking for a clear, simple definition.

mmmmmmmm.........When pertaining to multi-heat source systems, a series system is when all the flow goes equally through more than one heat source before going to the load whereas parallel piping flow is through only one heat source.

I strained on that one.

Mike

 

[stee6043]

My whack at it - if tanks (or anything else) are plumbed in series you go through one tank before getting to the second tank. In parallel you would go into both tanks at the same time and out both at the same time.

 

[Hydronics]

I believe the easiest to follow explanation is to equate it to a series versus parallel electric circuit which most people are familiar with.
Series is connected so flow goes through one first then the other. (positive connected to negative or supply connected to return)
Parallel passes flow through both simultaneously. (positive connected to positive or supply connected to supply)
Parallel drawn in a one line diagram looks like a ladder, series is a straight line (one in front of the other).
An electron (or water molecule) in series can pass through both devices, in parallel it can not.

A simple picture could explain this wordiness in seconds!

 

[in hot water]

With parallel you can run either boiler without having flow through the other. Or run both at the same time. The boiler only sees flow when it's circulator is running.

In series, flow is always through both or all the connected boilers.

This is an example of parallel piped boilers.

 

[WoodNotOil]

It is simplier than all that:

Series - Not enough heat to heat your house on really cold days!

Parallel - Enough heat to heat the house!

Sorry to be so cynical about it, but I have dealt with my series hookup for a few years and it does not work in really cold weather. The reason is the water returning from the zones mixes with the hot water from my wood boiler lowering available temp (10-20* per zone that is running).

Series - Supply to return
Return to supply

Parallel - Supply to supply
Return to return

Stay away from series hookups! I wouldn't have one if it were not for the Tarm manual suggesting it and it being what my installer was most familiar with. Tarm called it a "parallel hookup" but it was really series. I had wanted a P/S but my installer wasn't as comfortable with it. I believed my installer and Tarm and have had to live with it so far. I am going to a P/S or parallel hookup over the summer.

 

[steam man]

It is simplier than all that:

Series - Not enough heat to heat your house on really cold days!

Parallel - Enough heat to heat the house!

Sorry to be so cynical about it, but I have dealt with my series hookup for a few years and it does not work in really cold weather. The reason is the water returning from the zones mixes with the hot water from my wood boiler lowering available temp (10-20* per zone that is running).

Series - Supply to return
Return to supply

Parallel - Supply to supply
Return to return

Stay away from series hookups! I wouldn't have one if it were not for the Tarm manual suggesting it and it being what my installer was most familiar with. Tarm called it a "parallel hookup" but it was really series. I had wanted a P/S but my installer wasn't as comfortable with it. I believed my installer and Tarm and have had to live with it so far. I am going to a P/S or parallel hookup over the summer.

I 've seen your piping plan on your website. I am not sure I would call it a parallel or series hook up. A series hookup woud have the zone returns going to the Tarm return and as a parallel would have the supply to the supply as you say. I've seen the Tarm plan before and to me the wood boiler is more of a zone that adds heat to the system. I don't know how the returns mixing with the supply from the Tarm can be called a parallel or series hook up. The problem you run into is that you have to consider "mixing" temperatures". Without getting into a math problem, let's say all return flow from the zones is equal to the Tarm flow. The zones are at 140 or even 160 and the Tarm is 180, you will never get a mix temperature of 180 back to your zones. The way I see it is the Tarm would have to be somewhat hotter, say 190 deg or give more flow output at 180. I would guess that your problem is more pronounced at heavy loads. Either way I am not convinced the oil boiler is losing that much heat. There is a few things to consider with a series hook up. If either source is disabled or not up to temperature it can act as a heat sink. A cold wood boiler should not even be in the loop if that's the case. Ironically, if you take it out of the loop, do you really have a series hoop up? If both heat sources are active you should get more than enough heat. The fossil fuel should only come on at heavy loads. The downside is that you lose heat by keeping the fossil unit warm. The upside is that it stays warm thus no condensation, corrosion, leaks, and ready to.

Mike

 

[in hot water]

The only reason for series IMO, is boilers with tankless coils for DHW. They need to be kept hot to assure hot water.

Even so I would rather spend the time and money to eliminate the tankless coil, install an indirect tank or HX and storage, than to keep an unfired boiler hot just for DHW.

There may be a dozen way to pipe and control a multi boiler/ storage system. It really needs to be designed, sized, piped, and wired to your particular application. This includes pipe and pump sizing and loction, storage vessel design and size, etc.

It's the reason we see so many piping variations here, and also why it is a challange to come up with one or two generic piping and wiring schematic for folks to use.

I think it best to read up on basic piping concepts, their plus and minuses and chose the one that fits your job, and budget best.

Always keeping safety in mind, of course.

hr

 

[steam man]

[quote author="in hot water" date="1231621043"]The only reason for series IMO, is boilers with tankless coils for DHW. They need to be kept hot to assure hot water.



Good point. I didn't think of that since I have an indirect.

Mike

 

[razzorm]

I'm confused by replys saying series is second best.

It seems to me that water returning from zones will cool boiler temp. no matter where it goes.
Also wouldn't series hookup increase storeage capacity no matter how small it may be.

Just my thoughts.

Series hookup for 25 years and satified with it.

 

[Jackpine Savage]

I'm confused by replys saying series is second best.

I think it is less efficient because you are losing heat from the idle boiler. The boiler is radiating heat to where it may not be needed and also sending some up the chimney or out the vent.

 

[WoodNotOil]

A series hookup would have the zone returns going to the Tarm return and as a parallel would have the supply to the supply as you say.

I assume the reason this is not done is because if the oil boiler ran on its own you would not want the return water to have to pass through the Tarm cooling it.

The way I see it is the Tarm would have to be somewhat hotter, say 190 deg or give more flow output at 180. I would guess that your problem is more pronounced at heavy loads.

I do keep it at 190* just for that reason. You are right also that if I was willing to burn oil as well I would have no trouble keeping the house warm. However, I have a problem with the idea of my Tarm idling while I burn oil just because 3 zones happen to be on at the same time. I am unwilling to burn oil at all.

The only reason for series IMO, is boilers with tankless coils for DHW. They need to be kept hot to assure hot water.

This is the reason I have a series hookup, but plan to address this as well. I have coils in my Tarm and my storage tank, so turning off the one in the OB is no big deal.

I’m confused by replys saying series is second best.

It seems to me that water returning from zones will cool boiler temp. no matter where it goes.
Also wouldn’t series hookup increase storeage capacity no matter how small it may be.

Just my thoughts.

Series hookup for 25 years and satified with it.

Perhaps yours is piped differently than mine, but when the Tarm is up to temp I want that water to go directly to zones when they need it instead of mixing with return water. That return water should go into the Tarm when it is running and into the oil when it is not. I think Parallel is the way to do that. I don't worry about the OB losing some heat and keeping it warm probably maintains it better in the end.

 

[Hydronics]

[quote author="in hot water" date="1231621043"]The only reason for series IMO, is boilers with tankless coils for DHW. They need to be kept hot to assure hot water.

Actually, you can maintain temp. in the fossil boiler for the tankless coil in parallel. This is the preferred setup, it does require two circulators though, whereas series requires only one. The flow will be in reverse through the fossil boiler, more flow when no zones are calling.

 

[Eric Johnson]

My system is in series, in that I can't isolate the gas boiler from the system and still heat the house. In order for water to get back to the EKO or into the zones, in other words, it has to flow through the gas boiler.

Is that a way to define "in series?"

 

[Grover59]

I am not sure why this has to be so complicated, but I see the biggest reason someone may want a parallel set up, is so that they are not heating the fossil fuel unit and suffering the standby waste of that unit. If one had a cold start oil boiler then the parallel set up becomes even more of a good thing. At this time of year my oil boiler is always hot so the series works ok, I have a total of about 13 gallans of water combined with both boilers and the circulator runs 24/7. Maybe next year I will change to a parallel set up so that I have more flexability with how I can heat the house.

Steve

 

[Eric Johnson]

My main concern is that if my gas boiler ever springs a leak, I'm pretty much out of business until I can either replace it or re-pipe everything. That would be one long night. But other than that, I don't have a problem with standby losses heating my basement. And, as somebody pointed out, my 1958-vintage Weil McLain holds a lot of water, along with the 15 cast iron radiators that it serves.

 

[RJP Electric]

Yes Eric, If your gas boiler system and EKO is piped in similar to mine excluding the tank that is a classic series boiler setup. You are correct, if we spring a leak we are in trouble.

All I would have to do to make it a near parallel system is take the pipe that is below the main pump and bring it to the top of the oil boiler where I put the dashed arrow. The zone return water would still go through the boiler though. In order for a true parallel ladder NoFossil system, where the zones were totally isolated separately from the oil, wood and tank, I would have to redo the entire pluming and it was not in the budget.

We discussed this a few months ago in another thread. Some people don't like them in series due to a waste of BTU's through the boiler, heat up the stack or what ever the case may be. One thing is for certain I have plenty of heat, I got a kick out of it when Joe Browning called it brute force heating! When my block in my oil hits 150º I have an aquastat that shuts off the main pump and closes the zone valve and the hot block heats the house and the water is diverted to the tank. Plus when there is no zone calling the main pump isn't on either. It takes nothing to heat up my tiny Weil McLean boiler. Everyones setup, situation and budget is different, I don't know why most are against series setups. I wouldn't have it any other way.

 

[Eric Johnson]

As I noted earlier, I disable the gas burner at the beginning of the heating season and only put it back into service if we're going to be out of town for a few days, which usually doesn't happen (sigh!) in the winter. I stuff fiberglass insulation into the exhaust pipe and basically lock out/tag out the gas burner. I have an aquastat in the gas boiler vessel that keeps the zone pumps shut off until the temp in the boiler reaches 140. That way I'm always pumping hot water into the zones. Pretty simple but it works just fine.