A REALLY basic hydronic question

Scott_Mountain_View_CA

In theory I would agree, but there are plenty of times when we might want to throw the system out of balance intentionally such as rooms only occasionally occupied, an overnight guest that prefer's a warmer or cooler room, etc.

Mark Eatherton

"Yeah, I wasn't sure Mark understood what my objective was....sounds like he's doing something entirely different.

For a single zone residential design, I can't think of a good reason NOT to install TRV's on most or all rads (other than cost?)."

Scott, it was merely a suggestion, and not necessairly directed as you as much as other people considering the application, or a similar application. Just trying to educate.

I completely understood that you are trying to do this for as little money as possible because the house is going on the market. If you had 3 radiators serving one room, then my recommendation could cost less labor than putting one TRV per radiator, but then you'd have to re-arrange your piping arrangement to allow for a manifold, and home run tubing to the affected radiators. It's just another method for people reading the thread.

Honeywell aslo makes TRV's.

Food for thought.

ME

ME

Scott_Mountain_View_CA

I searched the web for a Design Day Temperature Table by city or zip code and found nothing. Any suggestions on where to get this data? I can estimate based on average lows, but the correct data is the .975 percentile number and that cannot be derived from averages.

Scott_Mountain_View_CA

I don't disagree with your pragmatic approach. On the other hand there is a precise science involved and I think it's worthwhile to at least attempt an accurate design, within reason.

Whatever I come up with will be better than the 2 knucklehead contractors that originally bid the job: Neither did a heat loss calculation and both SWAGGED a BTUH loss/sq' ft of 30, which is nearly double a reasonable calculated loss for my home. I figured they were sandbagging to save time and to avoid any chance of a call back for an undersized system. I've since found another contractor that understands the math and is helping with the boiler room part of the project.

The SlantFin HL software says my whole house average heat loss is 14 BTUH/Sq'. That seems really low, but I live in a temperate Mediterranean climate, and my home is very well insulated.

Scott_Mountain_View_CA

I do have a question about what Slantfin refers to as a 'cold partition' wall. Would that be an attached garage wall etc?

RobG

Scott_Mountain_View_CA said:

I do have a question about what Slantfin refers to as a 'cold partition' wall. Would that be an attached garage wall etc?

Yes, as long as the garage is unheated.

Tinman

What was the REALLY basic hydronic question?

Rich_49

What is your exact location ? I can easily give you that .975 percentile number .

Scott_Mountain_View_CA

Rich, I'm located in Mountain View, Calif. 94043

Thank you

Rich_49

Record low temp of 21*F . You don't need heat ! LMAO .

https://en.wikipedia.org/wiki/Mountain_View,_California#Climate

Design is 39*F w/ 22 mph wind . That was easy . San Fran nearest city I could access , ASHRAE number is up to date .

Scott_Mountain_View_CA

Stephen Minnich said:

What was the REALLY basic hydronic question?

Read the first post.

RobG

Scott_Mountain_View_CA said:

In a simple residential reverse or direct return system, what causes the water in the hot water pipe to divert to the radiator? In other words, what would cause the hot water to exit the 3/4" pipe at a tee and flow through the radiator? I understand how the water in the 3/4" pipe would want to divert enough flow to fill the radiator, but I don't understand the dynamic that would force it to circulate through the radiator and out into a direct or reverse return pipe with any velocity.

Numbskull question....but I don't know the answer.

This thread has really gone way past the "really basic hydronic question" It may be time to start a new post?

Scott_Mountain_View_CA

I'd prefer not starting a new thread because I don't want to lose the continuity and history. Early on I invited the mods to change the title.

When you think about it, this is an instructive forum so you would expect discussions to elevate in complexity as the OP moves up the learning curve.

Scott_Mountain_View_CA

I'm wondering how safe/desirable it is to have exposed wall panels operating at 160-170 AWT? Someone outside this forum made a comment to me today that this could be a hazard for small children and the infirm. I hadn't considered this in my design. Is this a legitimate concern? The same person said that for water that hot it might be better/safer to run fin tube baseboard, where human flesh doesn't make direct contact with the emitter. What are your thoughts on this?

Harvey Ramer

I was raised in a house that was heated by woodstoves. No one ever got a serious burn. If you touched it one time, you would never do it again.

Scott_Mountain_View_CA

Hatterasguy said:

Want to talk about tempering valves?

Sure, you start.

Rich_49

Scott ,

You live in an area with a record low of 21*F . Why on Earth would anyone even consider water in the upper temp ranges ? You will never need water north of 140* , if that at design . The rest of the season you'll be heating with water temps that you could bathe in .

People outside this forum are outside this forum for a reason , it's what you learn after you know it all that defines your true knowledge . This individual would seem not to know that heating is now done with very low water temps regularly and that the new goal is to heat with the coldest water possible and cool with the warmest water possible while still getting both jobs done sufficiently .

The panel rads offer room by room wireless zoning and heating only the areas that need heat at that moment in time . Comfort throughout with not much chance of one being burned .

Scott_Mountain_View_CA

Rich,

I suggest you read this entire thread to gain an understanding of my situation and the type of construction I'm dealing with here...slab and no attic. I understand the trend toward high efficiency mod/con technology running at low water temps, and I'm well aware of multi-zoning and wireless controls. I also understand the significant up front dollar investment for all of the above. Cooler water = higher emitter cost @ design. I'm selling the house in less than a year and heading into retirement. Sometimes financial realities trump what's cool (pun intended).

My design day heat loss is only 13 BTUH/sq ft...and the total envelope is only 1,467 sq. ft. Given the falling cost of natural gas and the mediterranean climate I live in, the annual cost difference between 140 degree and 160 degree water is spit in the ocean, which by the way is getting warmer along with the rest of the planet. And Al Gore says that soon your industry can drop the H from HVAC, bless his heart.

Rich_49

Scott ,
I have been following the thread . My statement was made to point out that whomever you were talking to may not be the best person . I am right now looking at quotes for panel rads and am guessing they may not be as costly as you believe .

Although the cost between 140 & 160 may be spit in the ocean right now it may not stay that way and 90% of home buyers are looking for efficiency . A quick search of panel rads , why and where they are used on this rock would quickly determine that they are in fact efficient . I have no idea of your budget but know from designing systems for folks for several years that the dreaded panel rad many times comes out the clear winner when compared to other emitters .

Reality is that your house probably does not need all that much emitter with a 39*F design day and an average in the 40's .

Scott_Mountain_View_CA

Rich said:

Scott ,
I am right now looking at quotes for panel rads and am guessing they may not be as costly as you believe .Reality is that your house probably does not need all that much emitter with a 39*F design day and an average in the 40's .

I've done a thorough heat loss calculation by room to determine emitter sizing at design temp and AWT. I've received emitter pricing from Runtal. The difference in emitter size(cost) between 160* and 140* is ~$1,000.

And if I understand this chart correctly, the efficiency gain between 140* and 160* is only 1-2%. The payback isn't dramatic.

Scott_Mountain_View_CA

Rich, all of your points are well taken. My situation is probably not typical: retrofitting existing slab construction with no attic. It's either piping on the rooftop or around the underside of the eaves. This setup puts practical limitations on design, and my decision is to go with a single zone reverse return. Home runs for each emitter just aren't practical.

My hesitation to go down to 140* and incur the cost of larger emitters is based on data showing that the operating efficiency curve doesn't show significant improvement until the water temp hits 130 and lower. My understanding is this is because the release of latent heat of condensation occurs at or below 130, the dew point of NG flue gas.

The backdrop for all of this is that I'm selling the house soon and have limited funds available for the various remodel projects that need to be completed prior to the sale.

Rich_49

Scott ,
140* is an average water temp . What this means is 150 from the boiler , 140 AWT in the emitters and 130* returning to boiler , condensing all the time . Your average water temp seasonally however I would guess in the low 100's for >90% of the season .
You may also be missing that a panel radiators output is also ever changing . Those same rads that you priced at 140* can be fed higher temp water and increase output while when lowering water temp the output decreases . just set the ODR curve properly and those smae emitters will output what they need to based on the AWT within them . Or not .

Scott_Mountain_View_CA

Rich, I think we beat this one to death. Efficiencies aside, hotter water = smaller emitters, cooler water = bigger emitters, to produce the same BTUH, would you agree?

Scott_Mountain_View_CA

It would be convenient in my single zone parallel reverse return system to Tee off 2 rads within a very short distance (6" to 12"). My hot water supply and return piping is 3/4", and I'd be teeing 1/2" rad supply/return. Again, 2 tees spaced 6" to 12" apart, each tee supplying a different rad. My total system GPM requirement is 1.84, and the existing pump overruns that by a fair amount.

Am I asking for trouble? Should I figure out a way to put more distance between the 2 supply tees?

Mark Eatherton

Shouldn't be a problem at all provided you maintain the parallel reverse return configuration.

ME

Scott_Mountain_View_CA

Thanks Mark. Another question: One of my radiator branches requires about 20' of supply/return off the 3/4 piping. Am I ok using 1/2" supply/return tubing for this distance?

Mark Eatherton

At a recommended flow rate of around 1.5 GPM for 1/2" pipe, at a 20 degree differential, it will carry around 15,000 btuH. The addition of the 40' of 1/2" pipe will create more resistance to flow than the other radiators, but you probably won't notice the difference in real time.

ME

Scott_Mountain_View_CA

To reduct the resistance, would it make sense to run 3/4" for 15 of the 20 feet for both supply and return piping to that outlier radiator? In other words, tee 3/4" tubing off both the 3/4" main supply and return, run it 15' and then reduce to 1/2" tubing the last 5 feet to the radiator?

This radiator is supplying 2,823 BTUH of the total house 19,713 BTUH.

Mark Eatherton

Running 3/4" where 1/2" would work will help IF you can maintain good sweep velocities in the tubing, or provide some other means of air elimination. Otherwise, air hangs up, and you end up with a whole other issue (air binding) to contend with. Honestly, I don't think it is going to make that big of a difference. Based on my long term experience, the real world, real time "load" is generally half of what it is calculated to be, and a minor reduction in flow will not be noticed.

There are a WHOLE lot of REALLY screwed up systems out there that still put out a decent amount of heat. At least you can sleep well at night knowing you did reasonable due diligence.

ME