Jump to content

Thermal expansion tank required?


Recommended Posts

New townhouse with a Rinnai heater feeding wall convectors and potable water through an AQ Energy "Heating Box" (actually a KyungDong KD-HBO100).

Click to Enlarge
tn_200962217933_090622M028x.jpg

46.19 KB

Click to Enlarge
tn_200962217948_090622M022x.jpg

64.48 KB

I've not seen one these boxes before, which appear to be a super-duper tempering/circulation system. Anyway...my issue is that there was no "normal" thermal expansion tank despite the presence of a pressure reducer at the water service entrance.

I googled info on the heating box and found that it does have an internal expansion tank.

http://lib.store.yahoo.net/lib/lowenerg ... manual.pdf

However, when I subsequently contacted a tech guy at KyungDong he basically informed me that the expansion tank in the box only serves the heating system and wouldn't take the place of a thermal expansion tank, if one were required. Unfortunately, I'm not totally convinced he actually knew what he was talking about.

I'm going to report the TX tank as missing, with the "option" of the builder supplying my client with good documentaion why one wasn't installed. Just wondering if anyone was familiar with the set-up and associated TX tank requirements?

Link to post
Share on other sites

Good question! This is from the pdf...

Thank you for purchasing the Heating Box Model KD-HBO100/KD-HBC100. This Heating Box provides a combination system (heat potable water and space) with just one heat source in convenience of simple installation. The unit consist with a high head bronze constructed pump to circulate water and built-in priority device for more effective distribution in domestic hot water. my bold

I'm assuming that is poorly translated Korean.

As far as I can tell, the main differences between the box and the usual on-the-wall plumbing are the built-in expansion tank and the "priority valve". As I pointed out, it's not clear if that expansion tank suffices. The priority valve sounds fancy, but is it needed? It also seems odd that besides the usual tempering valve for the potable water, there is a second one in the box for the heating water. Why would there be any need to temper the heating water when you can control that temperature at the water heater itself?

My first phone call was to the distributer who knew very little other than "We don't sell many of those." Not exactly a ringing endorsement!

Link to post
Share on other sites

Good question! This is from the pdf...

Thank you for purchasing the Heating Box Model KD-HBO100/KD-HBC100. This Heating Box provides a combination system (heat potable water and space) with just one heat source in convenience of simple installation. The unit consist with a high head bronze constructed pump to circulate water and built-in priority device for more effective distribution in domestic hot water. my bold
I'm assuming that is poorly translated Korean.
LOL,

When I was in Korea, I used to tell my wife that if Koreans really wanted their products to sell well in America or Britain they really needed to hire Americans to write their owner's manuals. I figured there was probably a boatload of money to be made doing just that. My wife thought I'd completely gone around the bend. I still think it's a good idea.

ONE TEAM - ONE FIGHT!!!

Mike

Link to post
Share on other sites

Ahhh. In my vernacular, it sounds like a heat exchanger; a way to keep the heating water separate from the potable water.

FWIW, these can usually be installed for a few hundred bucks. Looks like they may have paid a few thousand for that thing.

Wonder if it works any "better?"

Link to post
Share on other sites

Ahhh. In my vernacular, it sounds like a heat exchanger; a way to keep the heating water separate from the potable water.

No. it's not that. There is definitely no heat exchanger or separation of the water. As far as I can tell, it's basically just a pre-packaged circ pump and tempering valve(s).

Wonder if it works any "better?"

It "worked", but I don't know about "better".

Link to post
Share on other sites

I seldom see an expansion tank with an open domestic/radiant system. They are mostly found on closed loop systems around here.

The priority valve is needed to set a priority on who gets hot water first and the length of time or weight of priority.

For example, I have domestic as my first priority over radiant and fan/coil. However domestic over time looses it priority to radiant depending how I set up the 'weight' of priority.

So yes, a priority valve is required to set up a system that must satisfy two different demand loads.

Link to post
Share on other sites

Thanks Rob. It makes sense but I don't know about "required". I see lots of combo water/heat systems, usually with a storage type water heater. I don't think I've ever seen a priority valve before. The photo is of a fairly typical townhouse system around here (albeit tankless). Basic tempering valve for the potable water and a circ pump (on a timer) for the heating.

Click to Enlarge
tn_200962301416_ondemandheat.jpg

48.53 KB

Do you have a photo of your system? I'd like to see it.

Link to post
Share on other sites

I'm thinking the priority valve is required because the unit can't do both demands at the same time. So it needs something to tell it to do domestic for a given time and then switch to radiant and vice versa.

Priorities change according to the application

For instance, residential domestic is always first, we want to ensure enough hot water for morning showers etc. The boiler should recognize the importance of showers over radiant or fan/coil demands so we set the 'priority' accordingly and give it a certain weight so the boiler won't do domestic all day long and neglect the radiant portion of its work load.

But your place of business might be different. If you have overhead garage doors opening and closing all day long then you would prioritize the fan/coil as your main call for heat. The domestic would in this case be very low on the list, workers will just have to wash their hands in cold water but we can't afford to freeze the bay.

Here is a photo of my boiler room before drywall.

Download Attachment: icon_photo.gif MechRoom (Medium).jpg

78.45 KB

Download Attachment: icon_photo.gif MechRoom2 (Medium).jpg

82.66 KB

Download Attachment: icon_photo.gif MechRoomFanCoil (Medium).jpg

48.05 KB

This is the radiant transfer plates for main floor tiles.

Download Attachment: icon_photo.gif UponorJoistTrak1 (Medium).jpg

94.16 KB

Download Attachment: icon_photo.gif UponorJoistTrakLoop (Medium).jpg

43.47 KB

Download Attachment: icon_photo.gif UponorJoistTrakNInsulation (Medium).jpg

63.14 KB

Link to post
Share on other sites

The 'priority valve' is meant to give the domestic hot water priority if the house is calling for heat at the same time. I suppose you could rig it so it would give the house thermostat priority, but I've never seen or heard of it done that way.

I've also never seen one installed with a separate expansion tank. The one in Richard's photo looked OK to me.

Link to post
Share on other sites

Richard , I'm not sure it needs an expansion tank or valve if it has a PRV on the line. The PRV makes it a closed system, but it is not storing any water so you really have nothing to expand. The supply water is being heated as it moves through the coils in the unit and it keeps on moving through the tempering device.

Link to post
Share on other sites

Anyway...my issue is that there was no "normal" thermal expansion tank despite the presence of a pressure reducer at the water service entrance.

Don't remember if it was here or over at the ASHI board but we had a discussion about PRVs. I was under the assumption that you had to have an expansion tank because the PRV would not allow for opposite flow however Jim Katen informed me that they do make PRVs that will allow for opposite flow. I still recommend them though - it's good piping practice.

Link to post
Share on other sites

LOL...well, that is just a tad more complex than what I typically see.

That your own work Rob?

The boiler, primary, secondary loops and zones were installed by my genius radiant guy. I installed the domestic tubing, irrigation and the JoistTrak.

Incidentally, I opted for a system feeder to avoid paying the yearly backflow preventer inspection fee. There is no make up valve, double check valve or pressure reducer to the system.

Link to post
Share on other sites

Anyway...my issue is that there was no "normal" thermal expansion tank despite the presence of a pressure reducer at the water service entrance.

Don't remember if it was here or over at the ASHI board but we had a discussion about PRVs. I was under the assumption that you had to have an expansion tank because the PRV would not allow for opposite flow however Jim Katen informed me that they do make PRVs that will allow for opposite flow. I still recommend them though - it's good piping pratice.

That is true when you have a conventional water heater. But with a tankless, I don't think they need one because you have nothing to expand.

Link to post
Share on other sites

If by PRV, you mean a pressure reduction valve, there should be one on the boiler feed, but never one on the (domestic) tankless water heater feed.

Street pressure is between 60-80 psi, so you need a pressure reduction valve on a hot water boiler to step the pressure down to between 12-20 psi.

Water heaters are open and operate at the same pressure as the cold water system. If you put a pressure reduction valve on a water heater feed, you'd dramatically reduce the pressure (and the flow) and you would have a trickle at the showerhead.

You should have a pressure-temperature relief valve on any tankless water heater, no matter what.

Link to post
Share on other sites

If by PRV, you mean a pressure reduction valve, there should be one on the boiler feed, but never one on the (domestic) tankless water heater feed.

Street pressure is between 60-80 psi, so you need a pressure reduction valve on a hot water boiler to step the pressure down to between 12-20 psi.

Water heaters are open and operate at the same pressure as the cold water system. If you put a pressure reduction valve on a water heater feed, you'd dramatically reduce the pressure (and the flow) and you would have a trickle at the showerhead.

You should have a pressure-temperature relief valve on any tankless water heater, no matter what.

Not on the hot water tank itself Jim but on the city water line coming into the home. I'd say at least 60% of the homes I do have one installed (my home too).

The main problem is that *some* of the PRVs are one way flow only. When the hot water tank heats the water it needs somewhere to expand. With out the PRV it just expands into the city water system however when a one way PRV is installed there's no where for the expansion to go so the P/T relief valve starts to weep. An expansion tank will take care of the problem though. I'm sure I'm not telling you anything new though, more for the benefit of the new inspector(s) out there.

A few years back I was going round & round with the city water department. Out of the blue the water pressure coming into our homes (in the association) shot up over 100 PSI. My toilets were making a strange noise at the fill valves so I checked the incoming pressure. They'd work on it and a week later it would shoot back up again. We all have PVC piping here and one of the neighbors had a line burst, on the second floor, and it flooded out the home. The city water department would take no responsibility stating that anything mechanical can (and will) fail. Their right....

We had a meeting of the home owners association and it was decided to hire a plumbing firm to install PRV and expansion tanks in all the homes. It's good insurance and piece of mind.

Link to post
Share on other sites

Anyway...my issue is that there was no "normal" thermal expansion tank despite the presence of a pressure reducer at the water service entrance.

Don't remember if it was here or over at the ASHI board but we had a discussion about PRVs. I was under the assumption that you had to have an expansion tank because the PRV would not allow for opposite flow however Jim Katen informed me that they do make PRVs that will allow for opposite flow. I still recommend them though - it's good piping practice.

That is true when you have a conventional water heater. But with a tankless, I don't think they need one because you have nothing to expand.

I'm not sure Scott. Just the act of heating water will cause expansion but I guess it's minor compared to a 40 gallon tank sitting at 120° ??

I have 0 experience with tankless hot water systems. Sounds like good CE credit for ASHI.

Link to post
Share on other sites

Hi,

What Scott says makes sense. A tankless doesn't even come on until you turn on the tap and the pressure drops to activate it. There isn't any build up of pressure; the instant you turn off the tap, it shuts down and there is no continued heating of the water to cause it to expand.

ONE TEAM - ONE FIGHT!!!

Mike

Link to post
Share on other sites

Hi,

What Scott says makes sense. A tankless doesn't even come on until you turn on the tap and the pressure drops to activate it. There isn't any build up of pressure; the instant you turn off the tap, it shuts down and there is no continued heating of the water to cause it to expand.

ONE TEAM - ONE FIGHT!!!

Mike

I was gonna say....

Each heating/domestic system has different needs. Though, I haven't seen a consumer use tankless system needing an expansion tank.

Personally, I don't like the tankless method. Seems to waste energy when you have larger families.

Great for the cottage though, where the demand is low. [:-party]

Link to post
Share on other sites

Hi,

What Scott says makes sense. A tankless doesn't even come on until you turn on the tap and the pressure drops to activate it. There isn't any build up of pressure; the instant you turn off the tap, it shuts down and there is no continued heating of the water to cause it to expand.

ONE TEAM - ONE FIGHT!!!

Mike

OK...after pondering & googling this a bit more...

The code (UPC at least) doesn't differentiate between types of water heaters when it calls for a thermal exppansion tank, but it probably should.

I agree that if a tankless just serves the potable water it doesn't seem that a thermal expansion tank would be needed. Presumably when the hot water faucet is shut off there will still be a little latent heating at the heater, but I can't see that being a large amount.

If the tankless also serves hydronic heat, in a very basic set-up like the photo I posted around the middle of this thread, then I think it does need a TX tank. When heat is called for the first time, the tankless is going to heat all the water circulating in the hydronic piping, and I can see that increasing the pressure significantly.

In my original post set-up, I now strongly suspect that a TX tank is not needed because of the expansion tank in the heating box. I had reported it thus...

INVESTIGATE FURTHER and REPAIR?: Plumbing codes call for the water supply system to be fitted with a thermal expansion tank, especially in a closed system created by the presence of a pressure reduction valve (as fitted here). In this case there was not a normal thermal expansion tank but there is an expansion tank in the heating box. I have not seen this particular system before so I called KyungDong, the manufacturer, and spoke to a rep. Unfortunately, he seemed unsure if the box’s expansion tank took the place of a normal thermal expansion tank. I recommend you have the builder or installer document that a normal thermal expansion tank is not needed with this system. Otherwise, I believe one should be installed.

I'm still comfortable with that, although my "believe" in that last sentence is now very shaky!

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...