Heating control best option

[hagadan 0]

Hi all,

As I am new here, in this field also, I would need your opinion/advice on heating control best option (energy efficient).

I am thinking for the beginning to buy HCL, but for now I will point out shortly my heating system:

- 6 rooms with radiator

- 1 distributor with 6 ways with possibility to add actuator (Rehau/Heimeier 220v / 230v) on each heating circuit

- Gas boiler

1st option

- Each room with Fibaro multisensory FGMS-001 for temperature control

- 6 actuators on distributor controlled by 3 Fibaro dual relays FGS-221

- 1 Fibaro single relays FGS-211 to control the boiler (Start/Stop)

- No thermostat on radiator

2nd option

- Each radiator using Danfoss Z-Wave Radiator Thermostat (LC-13) or Radiator Thermostat STELLAZ

- Distributor all the ways “keep open”

- 1 Fibaro single relays FGS-211 to control the boiler (Start/Stop)

3rd option

- Each room with Secure SCS317 Programmable Thermostat

- 6 actuators on distributor controlled by 3 Fibaro dual relays FGS-221

- 1 Fibaro single relays FGS-211 to control the boiler (Start/Stop)

- No thermostat on radiator

Q1: Can I create delay between activation of actuators and boiler activation? Rehau/Heimeier actuators need approx 3 minutes for opening.

Q2: Assuming that we have 2 rooms, in one the temperature is raising (boiler is working), but meanwhile another room needs heating. This means that from second room boiler relay receives a second command for start, is this possible? (Wile relay is already “started”)

Q3: Assuming that heating is working in 2 rooms and one reach the temperature set up, this one will send command to boiler to stop wile second room still need boiler to be active, possible? (actually first room actuator will shut down)

Thank you in advance for your experienced advices.

Regards.

[Dalle1985 16]

First off, radiators NEED thermostats. Actuators are good for infloor heating because of the heat inertia, in other words, the floor absorbs a lot of heat from the floor. The heating is then controlled by meassuring the temperature of the return fluid. On a radiator, you only have a very small heat mass, and therefore, this won't work for you. If you control a radiator by means of an actuator, it will flood it with hot water, meaning most of the heat will just flow through the radiator. This means that both your radiator and your boiler will be operating very inefficiently effectively wasting energy.

So for radiators, you should always use thermostats mounted on the radiator.

As for your questions:

Q1: yes you can.

Q2: no problem, you just add a validation step to ensure that you only send the command if it isn't already on. But either way, it shouldn't really be bothered by you sending the command multiple times, so it doesn't really matter.

Q3: you'll be reaching the limit of what you can program with the HCL. In general, anything more than very basic on/off stuff should either be handled by a HC2 or a proxy scripting server.

[hagadan 0]

What will you recommend, Danfoss or StellaZ?

[Dalle1985 16]

Don't know the stellaZ, but I have good experience with the danfoss units. They also look better IMO.

[hagadan 0]

Thank you, I will go for Danfoss and Hc2.

[alex88 71]

The last post in this thread describes how I setup my heating system:

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I don’t understand Dalle1985’s comment about actuators being inefficient for radiators. My heating system worked basically in the same way before I added actuators. All that happens now is that I have the ability to turn the flow of water off for each individual radiator.

[Dalle1985 16]

Amilanov,

It is quite easy; underfloor heating adjusts the temperature, by adjusting the temperature of water flowing into your heating system. It meassures the return temperature of the water in the circuit and adjust the inlet temperature by means of a shunt valve. This way, you always have the perfect amount of energy flowing through your system. Therefore, you can just open or close the telestat (the actuator) without regulating it. This is already accomplished by means of the shunt. Alternatively you ahve a pinching valve on the return line restricting flow in the entire system. This is cheaper however, it isn't as efficient.

You can't do this with a radiator. The radiator will have very hot water coming in (determined by your boiler/HE temperature) therefore, you must ensure that the energy in your circuit is transferred to the room completely before it leaves the radiator. If you just open a telestat, it will deliver full flow immediately, resulting in very rapid heating, but also a large energy loss as water leaving the radiator is still hot. This gives hot returns to your boiler/HE which gives you a lower boiler efficiency. The result is that you waste energy. The thermostat is needed to ensure the radiator has the correct flow compared to the room temperature. This is why you install them in the first place.

So you might feel you are getting similar performance, but the fact is that due to the nature of the laws of physics, you will be wasting heat compared to running regulating valves on your radiators. Alternatively, you need to have shunts for each radiator... Which will in effect be the same as having one giant radiator for the entire house.

So for radiators, use thermostats. Then you don't need to turn off the flow using a telestat, as the thermostat does that much more efficiently.

[alex88 71]

Dalle1985

You definitely know a lot more about heating than me.

You got me thinking about this. My plumber never explained any issues with the design, so I decided to look up heating system diagrams. I now understand what you mean about the return being too hot now which means that the boiler will not go into condensing mode. I suppose the hotter I set my system the less efficient it will be.

Could I not make my system more efficient by turning the output valve down at the rads ie restrict the flow of water coming out to the return? It would slow down the heating of the rooms but would allow more heat to dissipate.

Either way it's too late for me to change now. I suppose I'm lucky I have triple glazed windows and lots of insulation throughout the house

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EDIT:

I just read an interesting article against using TRVs (

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) which is weird as most houses I have been in have them...

It also talks about adjusting the "output" valves to get an 11C drop across the rad which is similar to the question that I asked above:

"The mandatory use of TRVs has also resulted in a new generation of plumbers and heating engineers who have no interest in the traditional skill of balancing a central heating system by adjusting the lockshield valves at the opposite ends of the radiators to the main valves. Balancing the system to achieve an 11C drop across each radiator used to be an integral part of a plumber’s training, but is fast becoming a forgotten art."

I hope I'm not opening up a can of worms here

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[Dalle1985 16]

Hehe... The discussion is pretty complex, that is for sure. It is true that the perfect solution is to balabånce the heating system. The problem is, that trying to balance the system in our kind of climate is almost impossible as the heating requirement changes with ambient temperature, and as you probably don't want the same temperature in all rooms, that means that the balance will change with changing ambient temperature:

if ambient temperature is 10 degrees and room A should be 19 degrees and room B should be 22, then you can balance this by changing the relative size of the radiators. It takes approx 1/3 the energy to heat from 10 to 19 than to 22 (as heat loss increases exponentially with increasing temperature difference). But if ambient temperature is -10, then you need almost the same heating requirement to heat the two rooms. Now you have a problem because the radiator in room A is way to small.

This is why you don't do this anymore, but instead use thermostats (TRVs).

If you turn up the heat in room A, more hot water will flow through the radiator (as the actuator will open more often) and back to the return thermometer. The return will register lower energy yield (less energy transferred to the house) and thus request the shunt to blend in less hot water. This will mean that the inlet temperature will go down, meaning that the radiators in B won't get enough hot water, lowering the temperature at the return which will then request more hot water. This will result in your system going into something called a steady state droop where it will pulse between too much heat and too little heating in the rooms. This is why, unless you have a perfectly designed heating system (which no one has) the TRV will give you superior performance.

Messing around with home designed temperature systems is not for amateurs. I'm using intelligent thermostats with a heating scheduler which will ramp up the radiators slowly, as this is the only really big issue with thermostats; if the difference between the setpoint and the actual temperature is high, it will open up fully. Therefore, it will do the same as a telestat to begin with: dump in hot water wasting energy. Therefore, I've designed my heating scheduler to ramp up by 1 degree pr 15 minutes. That way, it will start heating 1 hour before the setpoint must be reached if it has to increase the temperature by 5 degrees. This circumvenes the overshot issue. But in general, a regulating valve is always superior to dumping valves.

[alex88 71]

...Messing around with home designed temperature systems is not for amateurs....

And there I was thinking I was paying professional plumbers to install my system

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Looks like I will have to do some research and figure out how to improve efficiency. That said the heating bill test this winter will be what really counts.

[Dalle1985 16]

Well... It depends on your heating source and how you are billed. We have district heating, and we are billed based on the MJ, but also on our temperature draw down. So therefore, if we have poor heating efficiency, we will get a penalty if the temperature draw down is too low. But if have a remote heating source and only pay for energy consumption and not for the draw down, then it doesn't really matter. If you have some sort of boiler, then it is probably going to cost you more to do it this way.

But yes... Paying a professional doesn't necessarily mean you get professional answers. It might be clever from an automation point of view, but not from a heating.

If you have underfloor heating, then you can use this setup quite well, but then you shouldn't be changing temperature at all as it is very slow at reacting to changes In setpoint, due to the large amount heat stored in the floor.

[alex88 71]

At the end of the day I'll check my gas bill at the end of winter

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Do you think my idea of reducing the output flow from each radiator will work to increase efficiency?

[Dalle1985 16]

If you can restrict the output flow, that will work just fine. The way to do it, will be to ensure that at the outlet from the radiator, the temperature should be as close to room temperature as possible while maintaining the temperature you desire. But remember, this must be adjusted regularly to compensate for changing ambient conditions. So all you are doing, is the same work as a thermostat on the radiator, but less efficient. However, if you only reduce it enough to reduce the flow enough to still let the radiator perform under all ambient conditions, you will still increase efficiency.

But anyway, if your gasbill isn't increasing, it doesn't really matter, now does it. But the theory of it will have that you will be using more gas to deliver the same heat energy. Again, coming back to the relationship between a heat exchangers efficiency and the temperature difference, it is much more efficient when you have a large temperature difference. Therefore, your gas boiler will have to work harder to deliver the same energy to the system if you only cool your radiator fluid 5 degrees, compared to if it is cooled 20 degrees.

[alex88 71]

Great. I will try it out.

I will go out on a limb here and say that my gas bill will be 25-50% lower that it was last year.

My old house was leaky (with very old single glazed windows) and had average insulation. The new one has triple glazed windows and more insulation than you can imagine in a a Victorian house.

Cheer

Aleks