Heating with Hydronics, best practices

There have been some differing opinions on the topic of hydronic heat distribution and how to best utilize water as a heat transfer medium, so I thought I would open a new topic where this could be discussed without hurt feelings about someone's particular design.

So I will start by posting what I believe to be best practices and then others who have differing opinions may post their own ideas of best practices.

If you look at my current project, you will see that I use a system that incorporates: solar thermal collectors, hi efficiency(96%) low mass boiler operating at peak efficiency through hydraulic separation with a super-insulated 80 gal DHW tank with 2 separate copper coils(one for boiler and one for solar), a flow adjustable, thermostatically controlled distribution manifold, pex-al-pex distribution piping with copper main piping and hi performance, low mass flat panel radiators. I also use ECM pumps on differential pressure control and a Tekmar 256 boiler controller.

With this design, we always operate at the highest efficiency possible, utilizing solar for DHW and heating when possible. The distribution manifold has thermostatically controlled valves, so the ECM pump compensates for this automatically in differential pressure control mode. The Caleffi hydrosep hydraulically separates the boiler from the distribution manifold and provides excellent dirt and air separation as well. All pex-al-pex distribution lines are run in a bundle to keep them warming each other and for ease of repair.

The low mass radiators heat up and cool down quickly so the room or slab does not overheat since the radiators are sized for the room they occupy. The high performance radiators also convect air through channels in the back, so the room may warm up even quicker. This ensures that you don't waste a lot of heat on rooms that are unoccupied.

John Siegenthaler has a great discussion on this here http://www.duluthenergydesign.com/Content/Documents/GeneralInfo/PresentationMaterials/2013/Day1/hydronics-siegenthaler.pdf

Criticism is welcome!

All Blessings,
Bill

Bill,

Do you happen to have a schematic sketch of your system? What temperatures does your system operate at?

What brand of DHW tank to you have? I have been looking for something similar, but am having a hard time finding anything. We are building a new house this summer and I want to ensure it is ready for a future solar system. I want to also incorporate a wood boiler at some point.

Why did you use a hydraulic separator? For high-efficiency, gas-fired boilers, the burner will modulate to meet demand, so the water flow should vary as well to maintain a constant delta-T. I know some manufactures do require near constant flow, which would then require a hydraulic separator, but I try to avoid those boilers. My concern is that the hydraulic separator will mix the primary loop, causing a higher return water temperature and therefore reducing your combustion efficiency. Remember with condensing boilers, once the return water temperature gets above the flue-gas dew point (typically 130°F - 140°F), the boiler will not condense, resulting in a max efficiency of ~82%.

In-Floor Radiant vs Radiators:
We are doing in-floor radiant. In my opinion, the largest drawback of these systems is poor response to solar heat gains and occupancy. The low mass/temp panel radiator addresses these issues well.

On the flip side, radiators are less effective at making the occupants feel comfortable. Low-temperature radiators don't really radiate, they mostly convect. A lot of wasted heat is trapped at the ceiling, not the occupant level.

High-temperature radiators (including stoves and fireplaces) have the issue of radiant asymmetry. One feels hot on one side and cold on the other side, which results in poor thermal comfort. This effect is worsened with cold, poorly-insulated walls. For whatever reason, this effect ins't an issue when the asymmetry is vertical. Humans have evolved to deal with this (hot sun above and cool ground below; cold night sky and warm ground).

The old adage "Warm feet, cool heads..." describes the physiology of human thermal comfort very well.

I'll post my design at some point to give you a fair chance to criticize my design.

That's funny you mention a John Siegenthaler presentation. I really enjoyed his wood boiler presentation.
http://www.nyserda.ny.gov/-/media/Files/Publications/Research/Environmental/high-efficiency-hydronics-wood-fired-boilers.pdf

Joshua Meehl wrote:Bill,

Do you happen to have a schematic sketch of your system? What temperatures does your system operate at?

Hi Joshua,

No I don't have a schematic yet or operating temps since the heating system is on the back burner until Fall. The system flow and temperature requirements will be determined by a hydronics designer/engineer that I have worked for many times.

Joshua Meehl wrote:
What brand of DHW tank to you have? I have been looking for something similar, but am having a hard time finding anything. We are building a new house this summer and I want to ensure it is ready for a future solar system. I want to also incorporate a wood boiler at some point.

It's a Solar Spectrum tank that I bought second hand from a guy who didn't want the hassle of integrating solar thermal into his hydronic system. I think they were made by Caleffi; it has a Caleffi solar pump station on it as well.

Joshua Meehl wrote:
Why did you use a hydraulic separator? For high-efficiency, gas-fired boilers, the burner will modulate to meet demand, so the water flow should vary as well to maintain a constant delta-T. I know some manufactures do require near constant flow, which would then require a hydraulic separator, but I try to avoid those boilers. My concern is that the hydraulic separator will mix the primary loop, causing a higher return water temperature and therefore reducing your combustion efficiency. Remember with condensing boilers, once the return water temperature gets above the flue-gas dew point (typically 130°F - 140°F), the boiler will not condense, resulting in a max efficiency of ~82%.

For high efficiency boilers, you pretty much always want a hydraulic separator to allow flow to increase without a large differential pressure across the high flow resistance boiler. With the separator, flow can ramp up in the secondary without lowering exit pressure at the boiler which can cause issues with particulate coming out of solution and causing buildup on the heat exchanger. This is especially critical in old systems that are impossible to get completely clean. The hydraulic separator also allows heating the house with solar thermal without running through the primary circuit. Return temps are also moderated through the hydro-sep because when return temp increases, the burner will turn down and regulate supply temps in the condensing range for, as you pointed out, max efficiency. There are other ways to accomplish all this, but I have found the hydro-sep to be the all in one answer to most low mass, high resistance boiler installations.

Joshua Meehl wrote:
In-Floor Radiant vs Radiators:
We are doing in-floor radiant. In my opinion, the largest drawback of these systems is poor response to solar heat gains and occupancy. The low mass/temp panel radiator addresses these issues well.

On the flip side, radiators are less effective at making the occupants feel comfortable. Low-temperature radiators don't really radiate, they mostly convect. A lot of wasted heat is trapped at the ceiling, not the occupant level.

Yes, slow response causes uneven loading and overheat at inopportune times. 73F, as pointed out by Mr. Siegenthaler in the article you linked, is not warm feet. I found this out the hard way when the heated floor and mod con boiler I installed did not provide the thermal comfort or max efficiency that I had promised. This is when you change your system; when you have dissatisfied clients.

Joshua Meehl wrote:

I'll post my design at some point to give you a fair chance to criticize my design.

I look forward to it.

Joshua Meehl wrote:
That's funny you mention a John Siegenthaler presentation. I really enjoyed his wood boiler presentation.
http://www.nyserda.ny.gov/-/media/Files/Publications/Research/Environmental/high-efficiency-hydronics-wood-fired-boilers.pdf

Yeah, John is awesome, I've learned a lot from him.

All Blessings,
Bill

sounds like you have a really knowledgeable designer.  As I was reading your initial comments this is exactly what I was thinking.. decent size heat storage.  single source pump and controllers per zone.  I have always thought that one pump actually draws much less power than several smaller pumps.  Zone actuators to control the flow.

For the most part I would say you have a very high tech, and efficient system with the exception of the low mass radiators. Your system is very similar to mine except that I went with in-floor radiant heat, the in-floor part being a concrete slab.

I eliminated the delay through high mass via a Taco 705-2 controller with multiple sensors. With them I can control the mixing valve via the temperature outside, the slab temperature, return water from the floor temperature, and main boiler loop, to allow the mixing valve to adjust the temperature of the water flowing through the floor on a minute by minute basis. I have zone valves, but honestly they are the dumbest part of the system, along with my thermostats. They tell the system when there is a call for heat, and could shut the system down, or the zone valves down, but honestly the PLC is so good at what it does, it regulates the room temperature not by water flowing through the floor, but by how warm the water is flowing through the floor. In other words there is no stop and start; if it is cold outside, the system ramps the water temperature up to compensate for the house losing heat faster, and lowers the water when it gets warmer outside. Through that I get a very consistent temperature in my house. With the mixing valve, it does not matter what is heating the water; condensing boiler, wood/coal boiler/solar, etc...

Another thing I added was a Taco Relay. That is wired so there must be two calls for heat in order to energize the system. I urge anyone to do that because it has saved me a TON of money. That is because of passive solar gain, and while my house is not designed for it, I went in a different direction and made my house super insulated. I live on a big hill and get slammed by the wind. Still the east and south side of the house gets warm from the sun, while the west and north sides are cold. IF I had not gone with that relay system, every time there was only 1 zone calling for heat, the system would start. Now it requires 2 out of the 3 zones to call for heat before the system energizes. With my Taco Zone Valve Control, I can see this happening via lights. A lot of the time there is a call from a zone for heat, but since the other is not calling for it either, the system remains idle, and idle means not consuming fuel.

I also added 400 ton of rock underneath my slab. Obviously it is insulated from the ground, but basically what I have is geothermal since I have so much mass spread over such a large area. When the power goes out for days, I have found I lose about 1 degree per day. It is great because while others in the neighborhood are scrambling to keep their pipes from freezing and to be comfortable, I am weeks away from that and by then the power will be back on, or I could just run the heating system off my generator.

But no matter how radiant heat is accomplished, there is no doubt that it is the best heat out there.