Sterling Unit Heaters

Zman

I am working on a property that has dozens of these unit heaters installed. http://www.sterlinghvac.com/steam-and-hot-water-unit-heaters
There are all different sizes, some are horizontal and some vertical.
They are presently piped with no zone valves, the fans are controlled with a local thermostat. The units are emitting heat 24/7/365.
The question is, how much heat do they emit when the fan is off? I am proposing adding zone valves to save the wasted heating and pumping energy.
Any takers?

mattmia2

You can probably approximate it to a similar length of fin tube.

Zman

@mattmia2
I was thinking of that as a last resort swag. I am hoping to get something more exact. They do give an EDR rating in the manual.

Alan (California Radiant) Forbes

The horizontal ones will lose more - faster convection. I'd venture 12% and the vertical ones 8%.
Zone valves makes sense as long as the maintenance cost is less than the fuel savings.

Solid_Fuel_Man

Could you reset the entire loop? Why is there heat 365 days a year? Seems like some front end work would save more energy. I just did an install with about 3 dozen Sterling fan coils, each with a zone valve and a strap-on aquastat. Seemed like a huge waste of parts and material. A line voltage thermostat controlling each room's fan(s) and outdoor reset seems to be more conservative.

This is just my seat of the pants guess, sorry I have no real data.

Edit: it was a spec. job, that I had no control over, otherwise it would have been done the way i suggested.

ratio

Loop reset with WWSD of the pump sounds a lot cheaper than dozens of zone valves. You might even get away with boiler reset if your boiler can take a low return temp.

mikeg2015

Adding zone valve just cost money and add more points of failure and a leak point. Probably better to spend the money on outdoor reset so less heat is wasted and boiler runs more efficiently. Pump could be switched to variable speed and controlled on delta T so less flow in mild weather when most are not running.

Also could add outdoor reset to the boiler. Probably only needs maximum temperature maybe 5% of the winter.

EBEBRATT-Ed

If the heat is running during the heating season what's the problem? You still need to heat the building, the heat is in the building it's not being lost. This won't save any money.

Zman

The heaters are tied individually into the main. There is no way to reset the heaters alone. The building has many emitters that will not work with an aggressive reset.

The heaters are located in an underground garage which only needs to be heated to 55 degrees. The heaters never run in the summer and the garage is 65+ degrees. In the winter the heaters only come on on the coldest day.

If you assume 10% standby loss, the (14) - 200,000 btu heaters are emitting 280,000 24/7/365. The quick math for turning them off just 6 months of the year would save ~$5k annually not including the electricity for the circs.

The question is, how accurate is the 10% number?

mattmia2

just thinking roughly about this, a gravity furnace or boiler is larger than one with forced circulation, but it isn't 10x larger, it is like 3x larger, so my guess would be that the 10% is a conservative estimate. there is probably something you could do with heat loss calculation of an area and indoor and outdoor temp measurement with the manual valves to a heater or group of heaters on and off to get a better estimate.

mattmia2

Or measure flow and supply and return temp to figure out how much heat it is losing.

Zman

mattmia2 said:

Or measure flow and supply and return temp to figure out how much heat it is losing.

Good idea. If they had installed balancing valves it would be easy.
I guess I could check the delta with the fan on vs off and figure a percentage difference. I think that would be close enough for my purposes.

GroundUp

200k output at 200* SWT and 47GPM, but what temp water and flow rate are being used here? Are you derating it? My first thought is skeptical of an underground parking garage having 2.8M worth of heat emitters in it. Second is 10% seems very aggressive from the unit alone. I just so happen to have a 200k Sterling unit in my shop on a 24/7 circ from an outdoor wood boiler with a thermostat running the fan, as you describe. According to the Quicksetter in that loop, I am flowing approximately 8 GPM of 170 degree water as of 10 minutes ago when I took these measurements and the calibrated thermometers are showing less than 1 degree differential, even with swapping them, and that includes 17 feet of uninsulated 1" Type L. My math says that's less than 2% standby loss including the ~1000 BTU lost from the piping, so overall roughly 1.5% standby loss if we're calling it a 200k unit even though the actual output is only ~120k. Even at 120k, that's 2.5%.

Zman

I know the water temp, I will have to swag the flow rate. I can read the delta p of the main circs and can estimate it based on delta p and the piping between point A and B. The rating of the heater and delta will help verify the flow . I think putting my data logger on the supply and return and estimating the flow is as close as I am going to get. I can put the logger on the unit near the door so I get lot's of cycles.

I don't think they need anywhere near 2.8 million in heaters, but that is whats installed.

BDR529

Keep boiler hot.
Unit heaters are hungry for BTU's..
Could just be placement of a check valve.

The question is can you build the better mouse trap.
And that would depend on how good it worked before the improvements.

Zman

BDR529 said:

Keep boiler hot.
Unit heaters are hungry for BTU's..
Could just be placement of a check valve.

The question is can you build the better mouse trap.
And that would depend on how good it worked before the improvements.

I honestly have no idea what you are saying....

BDR529

Sorry, if it works well why do you want to change it?

Start valving things might take hours to come back up to temp.

Solid_Fuel_Man

> @BDR529 said:
> Sorry, if it works well why do you want to change it?
>
> Start valving things might take hours to come back up to temp.

I dont thing with 2.8million worth of emitter there will be a recovery issue. Check out the first few posts about this.

ratio

Maybe invest in one of those Chinesium flow meters, the strap on ultrasonic type. That would certainly help figuring out what going on.

Zman

ratio said:

Maybe invest in one of those Chinesium flow meters, the strap on ultrasonic type. That would certainly help figuring out what going on.

I bought one of those a few years ago and promptly returned it. When I checked it against pipes with known flow rates (water meter) it was up to 30% off.

Zman

BDR529 said:

Sorry, if it works well why do you want to change it?

Start valving things might take hours to come back up to temp.

It is wasteful and overheats the space. The conversation the rest of us are having is:

• How wasteful is it?
  
• Is it worth zoning it or applying another solution?
  

I am being hired to determine how much energy is being wasted and what the associated costs and payback periods would be.
I am not very concerned about recovery of low mass emitters in a parking structure. We have plenty of capacity and are in an environment where temp swings are not a concern.

ratio

Huh, that's saddening. I wasn't expecting the precision to match a quality instrument, but I was hoping for ±10%—something usable at least.

Thanks for the report, I guess I'll have to start yearning after an expensive one!

Zman

I don't remember the exact model but it was one which was available under many brands and cost around $1,000.
I dutifully read the manual and tried it on a dozen or so pipes.
I am not inclined to think any of the portable ones are any better. Unless it is engineered and calibrated for a specific condition, I am skeptical.

GroundUp

In any parking garage I've ever worked in, the UH are always installed with motorized control valves and aquastats. Obviously temp control will be more proper that way, but for all the work that goes into converting the system over I feel the returns would be pretty diminishing. Would be a nice job though, if you wanted it! Does the heating system run all summer too? Maybe for reheat coils in the building or similar?

Zman

It is a 24/7/365 large condo building.
This whole exercise is to determine whether it is a good idea.
I find some of the responses where people already know the answer with no facts to be very interesting.
I will post the results when I finish so we can all learn from this.

GroundUp

We all know that's a big part of any trade, most don't care to open their mind or bother to even try to learn anything from others. Assuming flow rates are considerably higher in your application than mine, even if we call it a 5% standby loss it's a pretty serious waste in the warm season. If they don't need any automation for the system the price to add control valves and aquastats may not even be too bad, I'll be curious to see what you find out!

Solid_Fuel_Man

No way to isolate just the fan coils in the garage and valve(s) there? I assume the answer is no. They must all be tapped off in different areas where a main serves both garage and condo?

icy78

Maybe what you could do is tell the association.....if, the flows were balanced at installation, however that may have been done, and the output of the heaters is X with fan running, and the delta-t of the piping is X at the assumed flow, then this is the btu output without fan.? (Your measurement)
That gets you off the hook for having to read the flow rate, unless they want to pay for that.

Zman

I had a little extra time today and quickly put my dual temp thermometer on a couple units.
The delta T on the horizontal unit was 17 when the fan was on and 3 when the fan was off (~17.6%)
On the vertical unit the delta was 2.75 and 9 (~30%)
I am now inspired to dig deeper. I will bring the data logger out next week and put 2 probes on each pipe for super accurate and nerdy results.

icy78

@ Zman, got any super accurate and nerdy results?🙂