Author Topic: Hydronic heat experiment fail! Seeking suggestions on heating element doodad  (Read 532 times)

a_scanner_brightly

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Part 9187231 in the continuing saga, last post here
https://forum.mrmoneymustache.com/do-it-yourself-forum!/hydronic-heating-update-and-request-for-sanity-check/msg2168077/#msg2168077

Brief recap: I have a single-room hydronic heat system for a converted garage.  The PEX, baked into the concrete, only holds about 5 gallons of water.  I need to heat up 5, circulating gallons of water.  As an added catch, I only have a 120V, 15A circuit available at the place where I can add a heater.  This system used to work when it was open looped through the house's water heater, but when I bought it the inspector told me this is quite unorthodox and I agreed, so it was disconnected before we bought the house and we replaced the main water heater for the house.   I would later discover a lot of gross gunk in the water of the hydronic system, which confirms I made the right choice, and decided to redo the system with a separate, dedicated heat source.

I selected this Aquapower AQM 2-1 tankless, point-of-use water heater for the heat source:
https://www.homedepot.com/p/AquaPower-120-Volt-1-8-kW-0-27-GPM-Compact-Point-of-Use-Tankless-Electric-Water-Heater-AQM-2-1/206642687

because my rough mental estimate was that it should work.

Frustratingly, it almost works.  It heats the water in the system up to about 70 degrees (I'm in the Pacific Northwest, so that's more than the ambient temperature) and then it stops climbing.  It's not enough to change the temperature in the room.

The problem is that the machine is configured to output water between 90-100 max, and then it stops increasing it above that.  That is, the water gets put out at 90-something degrees and then by the time it circulates back, it's dropped to about 70 degrees.  I looked more closely at the box and manual and it seems very much like it does this on purpose, and that it's not configurable by the user.

So, I need to replace my heat source.  Any thoughts on what I could use here?

Again, the whole system only circulates 5 gallons of water.  Given the fact that I can use an electric kettle to boil a liter of water for tea in a minute or two, this seems like it should be possible.  I feel like the AQM 2-1 would have worked if not for a specific configured safety limit.

Product recommendations for what to use here? :)
« Last Edit: November 12, 2018, 11:40:40 AM by a_scanner_brightly »

J Boogie

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Live and learn right?

You need a different heat source. You are trying to heat your garage with a candle basically. You need to use more power, but you're limited to 120v 15a. Maybe there's an option that can work without having to run new wires.

There are a few things to keep in mind. Radiant floor systems require 85-125 degree water to run. That's a pretty big range and depending on your thermal mass, how cold you're starting at, how long your loops are, what your flow rate is, you'll want to set your aquastat somewhere in that range.

Your experiment has shown that 90~ degree water flowing at .32gpm is inadequate.

So if I were you, I'd find an on demand electric water heater that'll give you as high of a flow rate with as high of a temp as possible at 120v 15a.








J Boogie

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Specifically, I'd call up Stiebel Eltron and ask them what model of theirs could potentially work for you. They have great customer service from what I hear.

Good luck!

unpolloloco

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Can you run the water through faster?  If your heater isn't running at full capacity, this might help.  Your overall heating is going to be limited to 1.8kw, which is probably your issue, however...

J Boogie

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Not OP, but his unit has a flow rate of .27 gpm. He's gonna need something with a greater flow rate, and a greater max temp.

a_scanner_brightly

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Should the flow rate matter if it's recirculating?  As long as it's running the heating element at full blast it should be putting the same amount of heat into the system, whether it's increasing the output water's temperature a lot at a slower rate or increasing the temperature a little at a higher rate?  Since it's recirculating I figure it should eventually catch up, one way or another.

The problem with the current heater is that it backs off once it detects the output water temperature is within 90-100 degrees, which isn't high enough to make a dent in the temperature of the room.

This product looks promising.

Eemax Lavadvantage SPEX1812T S
http://www.eemax.com/products-for-you/lavadvantage/spex1812t_s/

Seems like it can reach 180 degrees output on 120V / 15A.  If used as a "booster".  Will shoot them an email and see what they say.
« Last Edit: November 13, 2018, 12:04:43 PM by a_scanner_brightly »

J Boogie

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Should the flow rate matter if it's recirculating?  As long as it's running the heating element at full blast it should be putting the same amount of heat into the system, whether it's increasing the output water's temperature a lot at a slower rate or increasing the temperature a little at a higher rate?  Since it's recirculating I figure it should eventually catch up, one way or another.

The problem with the current heater is that it backs off once it detects the output water temperature is within 90-100 degrees, which isn't high enough to make a dent in the temperature of the room.

This product looks promising.

Eemax Lavadvantage SPEX1812T S
http://www.eemax.com/products-for-you/lavadvantage/spex1812t_s/

Seems like it can reach 180 degrees output on 120V / 15A.  If used as a "booster".  Will shoot them an email and see what they say.

Max GPF isn't so much about how fast can the pump move water, but about how the heating element can handle water moving through quickly (without getting overwhelmed and being unable to heat it effectively anymore)

Looks like your new unit can raise the water temp 6 degrees at 2.0 gpf, which is a massive improvement.

If the flow rate is limited to .37, it's going to take a long time to heat up. The coils at the start of the loop might heat up a little quicker, but the ones at the end of the loop will only be getting lukewarm water for a while as the water is giving all its heat away before finally reaching them.

I imagine the max flow rate corresponds to the thermal mass of the heating element. A tiny heating element won't be able to retain heat as more and more cold water runs through it. A bigger one will be able to handle more and colder water.


« Last Edit: November 13, 2018, 12:53:24 PM by J Boogie »

Kahooli

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1) This is pex in slab. In a converted garage.
2) Radiant in the concrete is only going to work if it was properly insulated under the concrete. Was it?
3) Are you sure you've matched the amount of pipe/radiation to the heat loss of the room?
4) Your heater outlet water is only 90F? Or 90C?
5) I don't know how big this garage is, but 6000 btu/hr isn't going to heat a big space without amazing air sealing and high thermal resistance.
6) Do a manual J heat loss calc if you haven't already

(I am not any sort of expert on hydronics, I Am just an EE with a house that has steam heating, and I have learned a fair bit about different hydronic systems out of necessity. I'm asking these questions to get you thinking the way you need to - look at the problem scientifically)
« Last Edit: November 13, 2018, 01:00:36 PM by Kahooli »

a_scanner_brightly

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@Kahooli

This PEX system came with the house, although it was open looped through the old main water heater.  I have no idea if it's properly insulated in the concrete or not, nor do I know if it's properly sized.   I assume it used to work but it's possible someone just tried to foist their failed experiment off on us.  We decided to get the house anyway and re-evaluate our heating options for that room when the time came.

The water heater puts out 90ish Fahrenheit.   How did you calculate 6000 BTU/hr?

Kahooli

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The heater nameplate said 1.8kW.

1.8 kW * 3412.142 BTU/hr / 1kW= 6141 BTU/Hr.
The outlet temperature is a function of the flow rate, input energy, and the inlet temperature. The inlet temperature at equilibrium is a function of the radiating system heat loss ( and the heat loss of the room)

You're going to want to pick up a book on hydronic heating calculations before you waste too much money on things that might not solve your problem. As for the under slab insulation, You might find that information from the building plans filed with the county engineers office, or just might just drill a hole and find out.

I would note that heating this water loop with an electric resistance heater is going to be really really expensive. You can also heat the same space with a bunch of this sort of heater:

"https://www.amazon.com/dp/B07JVNFRDR/ref=sspa_dk_detail_3?psc=1&pd_rd_i=B07JVNFRDR&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=21517efd-b385-405b-a405-9a37af61b5b4&pd_rd_wg=756iY&pf_rd_r=8E91KKGX6NY1CQY04VGY&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&pd_rd_w=Bv28j&pf_rd_i=desktop-dp-sims&pd_rd_r=9b00ce5b-e793-11e8-b5ba-5dfed4e35b83"

for far less headache than trying to use the water loop. If you aren't plumbing that loop to a proper boiler, geothermal or electric heat pump, etc you are probably wasting your time and money.
Fill it with antifreeze for another day and plug it.

Kahooli

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How is the rest of the house heated? You say that it used to be heated open loop... which I agree is a huge no no. But does your main house still have an on-demand condensing boiler and controls for closed loop? Take a picture. =D

AccidentalMiser

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The heater nameplate said 1.8kW.

1.8 kW * 3412.142 BTU/hr / 1kW= 6141 BTU/Hr.
The outlet temperature is a function of the flow rate, input energy, and the inlet temperature. The inlet temperature at equilibrium is a function of the radiating system heat loss ( and the heat loss of the room)

You're going to want to pick up a book on hydronic heating calculations before you waste too much money on things that might not solve your problem. As for the under slab insulation, You might find that information from the building plans filed with the county engineers office, or just might just drill a hole and find out.

I would note that heating this water loop with an electric resistance heater is going to be really really expensive. You can also heat the same space with a bunch of this sort of heater:

"https://www.amazon.com/dp/B07JVNFRDR/ref=sspa_dk_detail_3?psc=1&pd_rd_i=B07JVNFRDR&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=21517efd-b385-405b-a405-9a37af61b5b4&pd_rd_wg=756iY&pf_rd_r=8E91KKGX6NY1CQY04VGY&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&pd_rd_w=Bv28j&pf_rd_i=desktop-dp-sims&pd_rd_r=9b00ce5b-e793-11e8-b5ba-5dfed4e35b83"

for far less headache than trying to use the water loop. If you aren't plumbing that loop to a proper boiler, geothermal or electric heat pump, etc you are probably wasting your time and money.
Fill it with antifreeze for another day and plug it.

The heater you have isn't remotely large enough to heat a concrete slab and room.  1.8 KW is equivalent to a stout hand-held hair dryer. 

I'd insulate the floor with a carpet and do what @Kahooli said.

J Boogie

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Can you share some of your insulation details?

Some garages have no insulation, some PNW folks are all about a tight envelope with plenty of insulation.

If you have an uninsulated metal garage door, your heat loss will be pretty significant given how large they are.

When you calculated your 90 degree water returned at 70 degrees, what was the outdoor temperature?



a_scanner_brightly

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How is the rest of the house heated? You say that it used to be heated open loop... which I agree is a huge no no. But does your main house still have an on-demand condensing boiler and controls for closed loop? Take a picture. =D

It blows heated air from overhead with a gas-electric furnace.    It was a retrofit, the house originally had a fireplace that's since been gutted.

I've been thinking of perhaps extending the furnace ducting into the room but since it's a converted garage it's a little more complicated.  The room gets *some* heating if we leave the door to it open.   Combining that with a space heater (below) might be the way to go.

I would note that heating this water loop with an electric resistance heater is going to be really really expensive. You can also heat the same space with a bunch of this sort of heater:

"https://www.amazon.com/dp/B07JVNFRDR/ref=sspa_dk_detail_3?psc=1&pd_rd_i=B07JVNFRDR&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=21517efd-b385-405b-a405-9a37af61b5b4&pd_rd_wg=756iY&pf_rd_r=8E91KKGX6NY1CQY04VGY&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&pd_rd_w=Bv28j&pf_rd_i=desktop-dp-sims&pd_rd_r=9b00ce5b-e793-11e8-b5ba-5dfed4e35b83"

for far less headache than trying to use the water loop. If you aren't plumbing that loop to a proper boiler, geothermal or electric heat pump, etc you are probably wasting your time and money.
Fill it with antifreeze for another day and plug it.

Ha, after seeing the supply house invoices add up I've been wondering if a space heater would've been a better way to go all along.

What's so sweet about the space heater you linked?   It looks similar to some wall mount versions I've seen...
« Last Edit: November 14, 2018, 12:37:19 PM by a_scanner_brightly »

a_scanner_brightly

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Can you share some of your insulation details?

Some garages have no insulation, some PNW folks are all about a tight envelope with plenty of insulation.

If you have an uninsulated metal garage door, your heat loss will be pretty significant given how large they are.

When you calculated your 90 degree water returned at 70 degrees, what was the outdoor temperature?

It's converted enough that it no longer has a door.  It seems like it has a bit of insulation, going by past experience rooting around near the outlets, but I haven't confirmed.  It's probably nothing awesome.

The 90-70 degree return was with an outdoor temperature of about 55.

a_scanner_brightly

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The heater you have isn't remotely large enough to heat a concrete slab and room.  1.8 KW is equivalent to a stout hand-held hair dryer. 

I'd insulate the floor with a carpet and do what @Kahooli said.

Indeed.  Eemax confirmed that we'd want to step up to 240V to have enough juice.  Looking at having to pay an electrician to probably upgrade the breaker box (it's full) to do this.  Meh.

Are you suggesting carpet because it's going to have a higher R-value than other kind of flooring, or just because it's cheaper?  I've been leaning towards some kind of laminate flooring that looks like hardwood, just to match the rest of the house.

Kahooli

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It blows heated air from overhead with a gas-electric furnace.    It was a retrofit, the house originally had a fireplace that's since been gutted.

I've been thinking of perhaps extending the furnace ducting into the room but since it's a converted garage it's a little more complicated.  The room gets *some* heating if we leave the door to it open.   Combining that with a space heater (below) might be the way to go.

Ha, after seeing the supply house invoices add up I've been wondering if a space heater would've been a better way to go all along.

What's so sweet about the space heater you linked?   It looks similar to some wall mount versions I've seen...
[/quote]

I was just linking the first google result for oil electric heater. There is nothing special about that one, and you can substitute anything you want in its place.

Since you have natural gas, you could get a condensing gas on demand water heater that might meet the needs (if the slab is insulated underneath and there's enough loops to be effective). This will cost more upfront, so youll need to calculate the ROI versus electric resistance heaters (depends on your specific utility rates).

I think you might be better served with ducting to the forced air furnace if your unit has the capacity.  Again, calc your ROI. Insulated flex-tube ducting isn't free but it's cheaper than any boiler. (It'll give you the opportunity to get up above the room and see how much attic insulation there is too!)

BDWW

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The heater you have isn't remotely large enough to heat a concrete slab and room.  1.8 KW is equivalent to a stout hand-held hair dryer. 

I'd insulate the floor with a carpet and do what @Kahooli said.

Indeed.  Eemax confirmed that we'd want to step up to 240V to have enough juice.  Looking at having to pay an electrician to probably upgrade the breaker box (it's full) to do this.  Meh.

Are you suggesting carpet because it's going to have a higher R-value than other kind of flooring, or just because it's cheaper?  I've been leaning towards some kind of laminate flooring that looks like hardwood, just to match the rest of the house.

Often you can replace full-slot breakers with half height. Might be an option to free up panel space.

Example:

https://www.amazon.com/Connecticut-Electric-General-THQP120-Circuit/dp/B000B7TG3O/ref=pd_lpo_vtph_60_lp_t_3?_encoding=UTF8&psc=1&refRID=P951J555JZ00Q9HM33AY

J Boogie

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Yeah, that's a great option to consider.  Here's a good article that'll help you determine whether or not you can do this.

http://www.startribune.com/how-to-know-when-tandem-circuit-breakers-can-be-used-aka-cheater-breakers/140688183/