How to design for different size zones?

Midnightsnacker41

Electrical Engineer here. So I'm familiar with circuit flow concepts, but have little plumbing experience. Been doing a lot of reading, but getting to the point of needing to ask some questions. 

I'm contemplating installing radiant heat in my house. It's a 70's ranch with a full unfinished basement. So I would install a staple up type system on the main floor. The plan for the basement would be when we finish it off to put it in a subfloor over 2 inch of eps insulation. So both floors would have a relatively low mass system.

I guess I was expecting to have a relatively high number of zones. This is the max I can see wanting to support, so I was thinking I would design for it:
1) master bedroom/bath
2) living room 
3) kitchen/dining room (fairly separate from the living room 
4) main floor bath
5) kid bedroom 1 on main floor
6) kid bedroom 2 on main floor
7) basement office
8) basement guest bedroom 
9) basement bathroom 
10) basement TV room
11) basement kid bedroom 3
12) empty space we might finish off 

Obviously some of these could be combined, but it still seems higher than the number of zones I see other projects mentioning.

My main point though is that there is a pretty big variation in those zone sizes, and I want to understand how to make sure they all get consistent heat. Let me start by explaining what I am understanding as the "ideal" system, and then ask my questions. 

An "ideal" system would have continual flow. That way there is always a little bit of heat going into each zone. If too much is going in, the system would decrease the heat a little, and if too little, it would increase it. That way the average input always matches the average output and the setpoint is maintained. If the system is too much of an on/off design, you will get relatively large temp swings. 

That is where outdoor reset comes in. It changes the temp of the water it is outputting based on outdoor temperature. For example, on really cold days you might need 120 degree water, but on milder days you only need 90 degree water. As long as 

Let's assume a design with a large Manifold on the secondary loop, and all zones coming off of it. Smaller zones would have lower resistance, and need less heat, so they would reach the max temp quickly. Larger zones would be slower to heat. So you need more flow to larger zones, and less to smaller ones. If you balance the flow properly, you could theoretically ensure that all zones are the same temp.

From what I am understanding, 1 way of doing zone balancing will have a single circulator pump for the whole secondary loop, and a balance valve on each zone. The balance valves are mechanically set once by the system designer so that smaller zones have an approximately equal resistance to larger zones. That way each zone gets an amount of heat that is approximately proportional to its heat loss. Then fine tuning is done with zone valves that are turned on and off by a thermostat.

Another way of doing zone balancing is having a circulator pump on each zone. This would increase the flow to bring the temperate up, and decrease it to bring it down.  

Questions:
1) Hydronic thermostats still just send an on/off signal, correct? So whether they are controlling zone valves or circulator pumps, you will still get them cycling some? Are there variable zone valves that can be used to just turn the flow (and lower the heat input to the room) on more of a variable scale? I'm thinking something like a PID controller, but haven't had much luck finding one. 

2) Am I over thinking this? Maybe the lower water temps caused by the outdoor reset means you won't have issues with heat overshooting the setpoint that I think you will. 

EdTheHeaterMan

This is the ideal design. But that will need some pretty sophisticated controls to accomplish that "Ideal" operation.

Electrically speaking (??? I could not get this next paragraph to post)


Practically, there are several less expensive designs that already work just fine.

Zoning should be approached based on how the rooms will be used, where they are located in reference to solar gain and how often they are occupied. So a layout of the Living room Kitchen and Dining room although separate areas, they are all used as one common daytime space, need not be separate zones unless kitchen has more Solar Gain from south facing windows, then it would be smarter to operate the Living and Dining room as one zone and the Kitchen as another. Otherwise, all three along with the bathroom should all operate as one zone. The kids' main floor bedrooms need not be separate zones unless one room is going to be a different temperature that the other.

Basement office, Basement entertainment room and Basement bathroom are going to be used regularly, so that is one zone the other two bedrooms cna be separate zones because one is not always in use and the other may need to be a different temperature then the other basement areas.

Since you are looking at radiant heat, you already understand that you don't set the thermostat and get the temperature you want instantly. Your change in temperature may take as long as 24 hours depending on the amount of the temperature change. You are definitely not going to use any timers to make the bedrooms cool in the day and warm at night. You pick a temperature and forget it. No auto setback with radiant


I hope this helps in your design.

hot_rod

The Euro systems are as close to ideal as I have seen when it comes to a lot of zoning.
They use predominantly TRV controls on panel radiators. A central delta P circ that runs continuously.
Heat source can be from a district system or a high mass or high volume condensing style.

A lot of zones or micro zones can lead to boiler short cycles, ODR helps. My ideal heater would be a tank style like HTP offers. You get ODR controlled modulation and 50- 80 gallons of buffer built in!

The zone controls that are ideal for this type of radiant system are like this Oventrop Unibox control. These are non electric, proportional, modulating zone controls.

As you can see a bit more involved to pipe in and design around this type of temperature control, but they are perhaps the ultimate control.

One central wall stat could turn on the boiler, or a well adjusted ODR would fire the system when the first heating day comes along

Delta P circ will wind down to a few watts of power consumption, durning the summer months barely spinning so they can detect TRVs opening and ramp to required flow rate.

Fine tuning can be done at the manifolds if you have widely different loop lengths.

What's in your wallet?

https://www.oventrop-us.com/unibox

HomerJSmith

Use Caleffi twist flow manifolds. Keep the loops at the recommended lengths for the size of the tube.

Erin Holohan Haskell

EdTheHeaterMan said:

This is the ideal design. But that will need some pretty sophisticated controls to accomplish that "Ideal" operation.

Electrically speaking (??? I could not get this next paragraph to post)


Practically, there are several less expensive designs that already work just fine.

@EdTheHeaterMan, we get a lot of spam about online poker, so we have a filter for the term. That's why your comment got held for moderation. I've sent it through. Sorry about that!

Rich_49

DESIGN for comfort before all else or it'll suck . Using constant circ and trvs on panel rads is great stuff with a tstat for or as a high limit . We have houses that only turn on based on the wwsd and run on odr for the length of season . If you're gonna do radiant make sure you only put rooms on same zones that are similar BTU sf requirements , similar finsh floor R values , similar use patterns and similar solar gain . If these are ignored the building will suck , PERIOD . Think about radiant ceiling for that basement also , keep as much headroom as possible . No , heat does not rise .

Zman

Lots of good info above.
Here are a few more thoughts:

• Bigger zones should have multiple loops. For 1/2" tubing, it is a good idea to keep the lengths in the 200'-250' range. If you can keep the lengths +/- 10%, balancing for flow is not that big a concern. If you do need to balance, there are tons of manifolds designed for that purpose.
  
• Doing an accurate room-by-room heat loss and altering your layout accordingly is a worthwhile endeavor
  
• Tekmar does make some slick controllers that will use outdoor temp, indoor temp, and even slab temp as feedback. It will use the info to adjust the supply water temp. I have found this much tech helpful in houses with high solar gain and high mass slabs. Much of the time it is unnecessary and a simple outdoor reset works great.