Any Heating System Experts out There?


#1

I’m trying to evaluate whether there is something wrong with the heating system in our vacation home. The home is in Pacific Grove, CA, which has some of the mildest weather in the world, since it is right on the Pacific next to Monterey Bay. Still, we need to heat it sometimes, since the temperatures at night can get into the 50’s and even high 40’s. We recently remodeled the 1200 sq foot building and due to California title 24 requirements, had to put in a super-efficient hydronic heating system. We have 3 heating zones in the unit, one for the main living area, one for the master bedroom and one for the second bedroom, each with their own Ecobee thermostat. Each zone pipes hot water to 2-3 fan convectors to heat the area. But the heating seems incredibly slow. It can take 8 hours, in the case of the living area to increase the room temperature 7 degrees, though with the outside temperature dropping by 10 degrees.

The graph below shows the 5 longest heating runs during the past month. Solid lines represent the room temperature minus the thermostat temperature (the number of degrees left before the room reaches the temperature the thermostat is calling for). The dotted lines are the difference between the outside temperature and the room temperature. Should it really take 8 hours to heat a room by 7 degrees ?

Graphs for the two other zones that are on the same boiler, and same boiler temperature below.


#2

What is the power consumption? Is the boiler gas or electric? If electric, did you do a quick ohm test over the elements (with power off)? Can you take a temperature reading on the water entering and exiting the boiler to get a delta? Can do this with a non contact infrared thermometer for $20. What is the rate of water flow? I added a $70 gauge to measure the flow on my geothermal system. While adding the gauge, I included a ball valve that allowed me to control the water flow.


#3

Also, please describe the water distribution system. Do you have a circulator for each heating zone, or a single circulator and zone valves? Are all of your zones slow to heat? Is airflow from your fan coil unit good and have you measured the air outlet temperature and/or any of the water temperatures?


#4

Thanks guys for your quick responses,

A few more details. The system uses an HTP gas-fired boiler/heater that supplies heating and supplies hot water to the building. The boiler feeds a manifold that fans out to the 7 fan convectors. Electronic controls near the manifold are connected to the 3 thermostats and open individual valves for each respective convector fan, plus send out a call for heat to the boiler/heating unit when any of the 3 thermostats is calling for heat. The boiler then heats and starts the pump to circulate through at least one zone of convector fans.

Pictures of the manifold and electronics below. It’s actually well instrumented with thermometers on both incoming and return pipes to the boiler, plus flowmeters on all the individual lines. I know that the individual valves are all working (several were initially stuck) and that water is flowing through within specs. But I don’t really know a couple of things.

  1. What should the operating temperature be when in heating mode ? The boiler let’s one set a linear relationship between boiler output temp and outdoor temperature. How do I know if my setting is right or wrong ?

  2. How do I know where the issue is, if the valves and the flows look OK ? If I poke around, it seems some of the convectors are less effective than others (some seem to put out less heat and the fans come on less frequently).


#5

Kevin, I know some about heating systems and about radiant heating, but I’m not an expert an anything. I do know that heat loss calculations (one that determines BTU requirement, heat loss, BTU available, rate increase, etc. is necessary to make a heating system fit your requirements. That needs to be done for each zone.

But, you have some impressive data there.

Your system is a more complicated one than I have seen or have. In our area, fan convectors don’t work well for we have faster extreme temperature changes than you do in CA. Convection heaters are not good at heating a room or area fast, especially if you have high ceilings or certain room configurations. Radiant heat can also be slow to respond. I suspect once the zone gets up to temperature, it stays that way well and efficiently. But high efficiency systems are not known for their speed of heating (or cooling) up areas - that frequently goes against being efficient.

Just some food for thought.

You should talk to a heating expert familiar with your system. The people who spec’ed your system for your new remolded home should be helpful. If they can show you the heat loss calculations, being a data type of guy, you may interested in it.

Just giving food for thought.


#6

This! Kevin, do you know how much gas is consumed?


#7

Good additional information. Looking at your picture, assuming a call for heat is active (which seems to be the case from the zone status lights) your loop supply temperature is only 100F and there is a very small delta T across your heating zones. I suspect you are pointed in the right direction looking at the boiler output temperature setpoint. The industry term for this is an “outdoor reset curve” and typically the curve is set so that the maximum design water temperature is reached at the minimum design outdoor temperature. Typical maximum boiler temperatures for conventional hydronic heating systems are in the 180-190F range. I would consider 110F to be a minimum useful loop supply temperature for mild outdoor temperature conditions. It looks like your outdoor reset curve needs to be adjusted, but you might want to consult your system installer/designer before doing so in case there are any limitations or other considerations in your specific installation.

Higher loop temperatures make for higher system capacity for obvious delta T reasons at the fan coil units. They also make for lower boiler efficiency, and thats why the outdoor reset exists–to keep the boiler efficiency it its sweet spot while still providing enough heating capacity for the outdoor conditions.

I would also recommend checking your fan coil units to make sure there are no blockages, dirty filters, construction debris inside, etc.


#8

Not an expert, but will note that we had an issue with our hydronic system’s efficient condensing boiler when the delta T between the outside ambient and interior temperature was too small to allow for condensation.


#9

Thanks @pswired, and everyone, for your detailed inputs and diligent questions.
I’m going to wisely take your advice and seek assistance from our installer.

@pswired, those photos may have been taken at a moment when the water had just started circulating so the 110 reading might be low compared to the boiler temp. But as you suggest, I think the real magic is getting the outdoor reset curve right. Originally, the unit was heating well in the winter, but the technician had left the outdoor temp sensor unhooked so the water was always at 180 degrees and heat was bleeding through during the summer, not to mention having uglier than expected gas bills.

@markhovis73, I’m going to review my gas bill today over the past year. I actually have two units set up the same way, but the downstairs has Nest thermostats that don’t allow export, so I’ll only be able to do the comparison on one.

Thanks and I’ll let you all know more data and results as they come in.


#10

@markhovis73,

I aggregated my heating runtimes into days, then graphed against gas BTU usage from my billing. I see a couple complications:

  1. The same gas system also provides hot water so some of those BTUs go toward water heating.

  2. Gas usage seems very coarsely quantized (always some multiple of 1.05 Therms). Makes for a very choppy graph.

  3. There are many days when the heating system is on for hours, but the PG&E gas billing shows zero usage, so there may be some delayed billing ?

  4. We also have days when the heating systems hasn’t run, but gas has been used - can be explained by hot water usage.

Nevertheless the data is positively correlated and adjusted R2 is about 0.4. The slope of the line about 170 BTUs (gas usage) per minute of runtime.


#11

OK, here’s the verdict from the the installer checkout. 3 adjustments plus one explanation.

First off the explanation - radiant heat of this type is slowwww but steady. Half inch tubing has limited heating capacity. I should be seeing a temperature drop between the supply and return lines of approx. 5-10 degrees when at peak heating. A 6 hour cycle should not be unexpected. I could probably figure out typical BTUs delivered per room if I watch the water flow closely.

System changes as a result of visit.

  1. One of the two living room fan convectors had zero water flow, hence no heat. The valve was open but the trim valve needed adjustment. Fan now comes on when the water flows through and warms it up.

  2. Output reset curve was adjusted to increase temp a little bit at the start of the curve (65 degree outside temp).

  3. Baseline “Away” heating temp was set to 67 degrees rather than 55 degrees. We have people in and out fairly regularly so this should help given the long heating latency of radiant.

Should be interesting to see how it plays out this winter.