Joshua Meehl

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since Jan 18, 2015
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Recent posts by Joshua Meehl


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.
9 years ago
Does anyone have any experience with wood gasification boilers? I am looking at units that burn cord wood, not pellets. Any recommendations on thermal mass storage is also helpful.

I am building a house this summer on the family farm. It is of conventional construction, but is designed to be as nearly passive solar as feasible for our climate. Heating will be radiant in-floor distribution with wood boiler plant with electric backup. Once we move in, I hope to tinker with solar heating, load reduction, PVs, etc.

I have a coworker that uses a Vigas unit with 500 gallons of water storage. I have now heard Garn works well (and they are local).

At some point I would enjoy tinkering with a RMH for outbuildings and greenhouses, but I need a reliable commercial unit (especially with a newborn on the way) for the residence.

9 years ago

Tim Malacarne wrote:I sure wish I'd of known about the oxygen barrier pex being so important, it's too late for me! Have a cast iron radiator for a heat absorber, and black iron pipe manifolds. How badly am I hosed? Is there anything I can do to combat the corrosion?

Thanks, I hope you don't mind my interjection....

Honestly with cast iron radiators and black iron pipe, you don't really have to worry about holes forming (maybe after 50 - 75 years). The main issue is the buildup of scale and sludge. A dirt separator (if you don't already have one) will take care of this, just blowdown a couple of times a year unit the water is clear. The Spirotherm units are not the cheapest, but will keep the system squeaky clean.

9 years ago

A heat transfer concept I find useful is THERMAL DIFFUSIVITY (α). It is simply the ratio of the THERMAL CONDUCTIVITY (k) over the THERMAL MASS (density (ρ) times specific heat capacity (c)): α = k / (ρ * c)

A very low diffusivity is great for thermal storage and very high diffusivity are great for radiators. A concrete/masonry/stone has five times the diffusivity of water (or sand with very high water content), so it is much better for heating a space. Water is better as a thermal storage medium, since it dissipates less heat per unit mass.

Another point you bring up is the benefit of hydronic radiant heating vs forced air heating. Water has ~3,400 times the thermal mass compared to air (62 BTU/ft3-°F vs 0.018 BTU/ft3-°F - pardon the vulgar Imperial units). Essentially you can transport the same thermal energy with a 1/2" diameter pipe as a 24" square duct. For energy usage, it takes 1/340th the energy to transport that heat (21.0 BTU/w-min-°F vs 0.0612 BTU/w-min-°F), assuming 22 w/GPM pumping power and 0.3 w/CFM fan power per ASHRAE STD 90.1.

9 years ago

Karen Walk wrote:

For your outdoor boiler - what are you using? Are you using a system that has a hot water tank for thermal storage? I have a Garn at my house - and it works great. 1800 gallons of water storage. Tarm boilers can also be provided with a thermal storage tank. If it's sunny in the winter, we can let our Tarm coast for a few days. When it's cloudy, we fire every day.

I am still shopping around for boiler, so I am going to check out the Garn and Tarm units. I was going to have the local welding shop retrofit some old propane tanks for HW storage. I want to add solar in the future. Early and late winter are typically cloudy, but mid-winter is too cold for clouds, which is fortunate (I guess). I'll have to explore to see if there is already a similar thread for these systems.

Karen Walk wrote:
Also, for Mark's slab - are you suggesting installing temperature sensor in the slab so that he has the option to control the radiant based on slab temperature? I think that's what you meant...

You are absolutely correct. That control scheme only really makes sense with a slab temperature senors, not a space temperature sensor (thermostat).
9 years ago

I am going to be installing a very similar system to yours, except with an outdoor high-efficiency wood-burning boiler. I am a consulting engineer (PE) that designs commercial HVAC and plumbing system, so I though (over-thought?) very long and hard on the most appropriate systems for my house.

To answer one of your original questions, you definitely made he correct choice with the PEX with oxygen barrier. Any space heating system should have this to protect the ferrous components. DHW systems do not need the PEX oxygen barrier, since DHW heaters come with anode protection.

To address earlier aired concerns about expansion/contraction of piping in-slab.: It sounds like your slab heat is for floor-warming only. The following sequence of operation should eliminate any associated issues:
1) I would suggest operating this at a constant temperature setpoint throughout the heating season (no temperature reset at night, etc.).
2) In the shoulder seasons during system startup/shutdown, I would suggest ramping up/down the slab temperature setpoint a couple degrees a day, to minimize the effect of the thermal expansion differential between the concrete and piping (and minimize slab cracking).
3) Verify if your pump selection has constant delta-T control (Taco FloPro or similar). This will ensures both the supply and return water temperatures are held constant. It will also result in the lowest energy usage by the pump. I can help you with the pump selection if needed.

I hope this adds some confidence to your project.

9 years ago
To avoid plastic, I would recommend cast iron (ASTM A74) DWV piping. It can expensive.

Don't use steel or copper piping, since drainage piping "breathes" and will result in corrosion.

As far as "less bad" PVC, be sure it is certified NSF Standard 61 compliant. This standard ensures that the plastic is rated for potable water with minimal leeching. Note that typical DWV PVC will not be rated per NSF 61.

For exterior applications, a classic french drain would work well. 1) Dig a trench 2) line with impervious material (clay) 3) backfill with coarse gravel.

Those are my 2-cents as an engineer.
9 years ago
Peter & S Bengi - Thanks for the feedback.

I have been reading on propagating hybrid poplars. I can get a bunch of cutting and go from there.

I have been looking at sunflowers as an oil crop, and there are some tall varieties on Seed Savers Exchange that are reasonably priced for broad acre applications.
9 years ago
Does anyone have any good information regarding a "windbreak guild"?

My wife and I are building a house this summer on a plowed barren field. I want to get a shelter belt established this spring to help prevent our house from getting blasted with cold prairie gales this upcoming winter.

I was thinking some sort of successional windbreak like:
Jerusalem Artichokes -> Nanking Cherry -> Cottonwood/Birch -> Norway Spruce

Also suggestions for nursery plants or other guild companions would be useful too.

9 years ago