Hydronic radiant thermostat

[birchlake]

I'm very familiar with the -FE18NA, even had one installed at my mother's place last year, and they're one of the most popular units for heating Net Zero Energy homes in New England as well as other high-performance houses. A friend installed three of them on a 3-family that I helped him do a deep energy retrofit on last year. They are reasonably "smart" units, and designed to take it at low temp. As I understand ti the automatic shut down at about -18F is to self-protect from damage related to mechanical tolerances of the metals in the bearings and compressor. They have modulating internal resistance heaters to keep them in mechanical spec, but not enough to run the at any arbitrarily low temperature. I have no issue with just letting them bounce off the bottom of their spec rating, since they're designed to self-protect. I believe Daikin has similar cold-temp auto-protections built in, but I don't know at what temp they kick off. If they work for central ME and northern VT (where excursions below the self-protect temp are common enough) they'll work in Melrose MN. (IIRC BadgerBoilerMN has an FE18NA too, but only uses it primarily for air conditioning, his being a hard core wet-head & all. :-) )

You're not really losing efficiency by letting an electric boiler cycle, and mechanical stress & degradation from thermal cycling isn't really all that much either, at the temps you're talking. How often does it cycle during the shoulder seasons at the 114F setting, and how short are the "on" cycles?

Dana,

I really like my Mitsubishi mini-split. The only issue I've had with it is a bit of a rhythmic ticking from the inside unit that was an annoyance. Ended up having to put shims on all corners of the inside unit to eliminate the vibe/tick. Other than that, it really works well for both heat and air conditioning, along with being very energy efficient as you mentioned. And you can't even hear the thing run outside; can't believe it is that quiet! Next winter, I will try experimenting with running the Mitsubishi a little deeper into the colder temps to find my comfort level with it before I start relying solely on my in-floor heat.

As for cycling of my Electro Industries boiler, when the outside temperature is in the 20s and 30s, it doesn't actually cycle that often at 114F, maybe every 8-12 minutes or so, but what I found weird is that when it does cycle on, it (sometimes) only runs for 1-2 minutes, then cycles off. I haven't tried it at 102F in this weather, but am thinking about trying 102F and observing how long the cycles are at that temp. As you mention, with solid state circuitry the wear and tear on the boiler is minimal, and although the boiler contactors are racking up a few more cycles at the higher temp setting, I would think the contactors are possibly rated for millions of cycles?

I just wondered which boiler temp setting would be the best compromise for boiler efficiency and reliability and energy efficiency. But sounds to me like it might be six of one, half a dozen of the other?

Thanks for the advice guys.......making the turn from "forced air" to hydronic in-floor and mini-splits has been a learning experience!! (but a good one)

[Dana]

Mechanical contactors do have a limited lifespan compared to solid state switches, but have lower on-resistance than SCRs and IGBTs (cheap solid state power switching) or all but the best FET technology (more expensive solid-state switching). I would assume the contactors are a replaceable part in this unit, at any rate(?). If it's incurring only 5-6 cycles an hour (which it sounds like) don't sweat it, but if it's ever finds a mode where it's doing dozens per hour it's time to do something about it. If there is a way to adjust the hysteresis in the controls to increase the minimum on-time it's the right thing to do. You might buy a little bit out of increasing the flow rate too, or not- it depends on how internal controls of the boiler determine when to turn on & off.

With electric boilers the efficiency is going to be the same at either temp, independent of the number of cycles it's running.

Even though the heat delivery is via air, heating with mini-splits has very little in common with ducted air systems from a noise & comfort point of view! Being fully modulating systems with variable blower speeds you don't get the undershoot/overshoot hysteresis in traditional bang/bang on/off single stage hot air furnaces or even 2 stage furnaces- room temps are very stable, with continuously sensed and adjusted input & output air temperature control. In the outdoor unit scroll compressors, variable refrigerant volume, and fully variable speed DC ECM-drive fan motors takes all the rattle & hum out of those too, making them ghostly-quiet compared to their traditional single speed reciprocating compressor AC-drive fan ancestors! The interior head of the -FE18s are significantly quieter than most refrigerators when the blower is at low or mid-speed, but it can get pretty gusty sitting in front of the head when maxed out (but still nothing like the rattle & roar of a 1-ton window AC unit.) Heating with mini-splits is nowhere near as cushy as radiant floors, but it's still a huge upgrade in comfort from heating/cooling with old-school ducted air systems.

[BadgerBoilerMN]

I agree. I have let mine operate below zero F, when I'm away, as it is naturally more efficient than the direct resistance boiler set at a backup temperature. We have seen no issues in our modest winters -15°F this winter in Minneapolis.

[BadgerBoilerMN]

Just to be clear. Your problems arose from the recommendations of a misinformed "radiant floor designer". I have no problem with Tekmar as I have been using them for about 20 years now. The problem I have is misapplication of them. There are virtually no good applications for a slab-only radiant control system residential space heating. Adding slab sensing can enhance comfort if properly integrated with ambient air temperature response. Your lead and lag are typically caused by solar gain and inappropriate design water temperatures. You have it right. Without the benefit of ODR, available with certain Electro models, you may want to switch temps up and down with the season. I even fiddle with my own EB-MO-10 on occasion as it is not as responsive as my condensing boiler controls. Still with a standard room thermostat and ODR the average fella will be more than happy.

Glad you are happy with the 522, Tekmar rules.

[birchlake]

Badger, Dana

Thanks for the information and advice guys. I have a better understanding now of my system (and design limitations as noted; no ODR, etc.) and how to best utilize it.

One final question. I have a combination of carpet and high quality sheet vinyl on my floor. I have read on different websites about "maximum temperatures" for vinyl. Some say 85, some say 90. I took my infrared point and shoot thermometer around my vinyl this morning and with the boiler set at 114 F and running, the surface temperature of the vinyl varies between 75-83 in most areas of the vinyl.

But I do have two small rubber backed rugs (recycled tire rubber backing) at the entrance to the patio and entrance doors and under those rugs, the temps are 85-89 degrees. It looks like the rugs are trapping some of the heat from radiating up and out and that is the cause of the elevated temps only in the area under the rugs.

Anybody think that this is going to be a problem for the vinyl under the rugs (ie; premature discoloration, drying out vinyl, etc)? Or is this close enough to the general heat spec. for vinyl and so should be okay? Any general thoughts on the use of vinyl floor coverings with hydronic radiant heat?

UPDATE: Found on the Mannington website (mfg. of my vinyl) that my vinyl has a high spec. of 90 degrees when used with any hydronic heating system. So even at 85-89 degrees, I'd still be within spec, but just barely. Looks like most vinyl is spec'd in the 85-90 degree range.

[birchlake]

Okay, before I let you guys go, I'd like to bend your ear with one more question. This one regarding my Tekmar thermostat.

I was just reading my installation and operation manual for my Tekmar 552 thermostat and have a question on one setting that I don't fully understand. The setting is W CYCLES PER HOUR. Here is the information on the setting in question from my installation manual.

W CYCLES PER HOUR: Select the number of heating cycles per hour.
SYNC = Synchronize thermostats to a 20 minute cycle.
AUTO = Automatic cycles per hour to minimum temperature swings.
RANGE = SYNC, AUTO, 2-12
DEFAULT = SYNC

My stat has been set to SYNC since installation last fall and it has worked pretty well this past winter. My understanding with the SYNC setting is that my boiler would only cycle on a maximum of 3 times per hour; is that correct? So SYNC with a single stat is the same as setting it to 3? Having the stat set to SYNC is probably why I don't see much cycling of the boiler.

Any thoughts on whether I should try the AUTO range for more precise temperature control or any of the other preset numbered ranges for my setup? Or just leave well enough alone with SYNC?

Thanks.

[jadnashua]

IF the house is comfortable and you do not notice the fluctuations between heating cycles, more cycles is not a good thing! Fine temperature control may work better with FHA systems rather than radiant, especially where you have a big heat sink of a slab.

[birchlake]

IF the house is comfortable and you do not notice the fluctuations between heating cycles, more cycles is not a good thing! Fine temperature control may work better with FHA systems rather than radiant, especially where you have a big heat sink of a slab.

Jim, I think you're right. As long as my house has stayed comfortable with only a small amount of temperature overshoot and undershoot, I'm going to leave my stat on the SYNC setting for cycles per hour.

It's taken me some time to figure out my first radiant system, but I sure do love it. Right now I'm sitting in my kitchen with my bare feet on the toasty warm floor while we're having a blizzard outside. It's a good thing!