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Old 01-28-17, 02:20 AM   #1
Acuario
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Default Predicting future heating/cooling needs

Under floor heating/cooling is great but is very slow to respond to changing load requirements, typically (in my case) response times are 1-2 hours.

When there is a meteorological temperature change the loading requirements on the system also change. As I don't have individual thermostats controlling flow rates through the collector valves the change is notable. As I attempt to run the water at the minimum temperature required for comfortable living (= least energy consumed and no mixer valves to control maximum temperature) I have to increase the required water temperature and/or switch on the second heat pump to give a boost. This then takes time to take effect, typically 1-2 hours.

I got thinking, wouldn't it be cool (excuse the pun) if I knew future predicted temperatures I could automatically adjust the temperature to cater for the lag and thus not have to manually adjust things.

So much exists on the internet now so I went looking for a weather feed and found one at –°urrent weather and forecast- OpenWeatherMap, they provide a 3 hour (as well as many more) forecast, perfect for my needs.

Next up (while I'm waiting for the pressure sensors to arrive for the defrost project).. see if I can integrate the feed into my controller.

Acuario

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Old 01-28-17, 06:07 AM   #2
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Acurio,

"Anticipatory" HVAC is becoming more popular. This is essentially a "set back" (set forward?) thermostat coupled to environmental, demand, and other needs/loads.

First, you need to know the time constant of the system - which you understand. Next look at daily weekly and monthly averages as a first pass. For example, in some situations, cycling off the floor heat during the M-F daytime might be appropriate if the time constant for reheating is short enough.

Then there are weekend settings to contend with. Am I home or am I on holiday?

But you are right in the area where lots of research is going on. Wind farms are using exactly this concept to allow better utilization of changing (future) winds. There is a whole set of so called "fuzzy logic" that can be employed to couple likely future changes in temperatures with your zone valves.

Where I live in central Oklahoma, we are subject to significant temperature swings depending on the jet stream above. I have seen a 40 F drop, in just a couple hours, many times. The weather people plot this and tell you "when" the cold front arrives.

But integrating the predictive data into a logical zone on or off (or even harder, a proportional controller), can be tough.

What are your ideas to turn on (or off) your valves?

Look forward to hearing it.


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Old 01-28-17, 08:00 AM   #3
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Hi Steve,

a fairly simple control for starters. Basically I have heat sources (Solar panels, 2 x heat pumps, oil boiler).

The solar works when there is sun, next the heat pump(s) and as a last resort the boiler. I aim to maintain the water temperature fed to the floor typically at between 31 and 34 degrees which is good for 'normal' days. The problem is when we get very cold and/or windy days, then I have to increase the floor temperature up to around 38 degrees.

The sources (with the exception of the solar) are set to operate at minimum temperatures to maintain the desired temperature, they switch on/off depending on the water temperature flowing to the under floor heating.

Now I have introduced a dew point monitor I also have room temperature to add into the equation. This will enable me to control a bit better the heat sources when the room temperature drops.

The problem that remains is the latency of 1-2 hours for the floor to catch up, this is where the predictive bit comes in.

I don't have any zone valves so my plan is simply to increase or decrease the maximum desired water temperature generated from the heat sources.

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Old 01-31-17, 09:56 AM   #4
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Quote:
Originally Posted by Acuario View Post
Under floor heating/cooling is great but is very slow to respond to changing load requirements, typically (in my case) response times are 1-2 hours.
Acuario

John Siegenthaler, the hero of high-mass heated floor hydronics for the USA, has recently been giving quite a few seminars on the topic of quick-response low-mass hydronic heating systems.

Lots of emphasis on hydronic radiant ceilings, hydronic radiant walls, high-efficiency low-mass low-temperature active radiators (with small fans).

I can imagine how some of these ideas could be combined with your predictive scheme.



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Old 02-01-17, 02:39 PM   #5
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I like what you are doing, Acuario I would like to do something similar, if I get ever get back to working on my Arduino-controlled thermostat.

Are you planning on keeping the water temperature in stiff sync with the (planned) outdoor temperature, or will there be some kind of more complicated time lag?
I guess this would depend (among other things) on your thermal mass: I have noticed that in our house, the water temperature needs to stay higher for up to 1-2 days after the outdoor temp has risen, before our heating system "gets the cold out of" the house's thick, brick walls.

If your house has less thermal mass, then it will react much quicker to the temperature swings, allowing you stay in closer sync with the planned, and real, weather forecast.
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Old 02-02-17, 04:45 AM   #6
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Quote:
Originally Posted by Acuario View Post
I aim to maintain the water temperature fed to the floor typically at between 31 and 34 degrees which is good for 'normal' days. The problem is when we get very cold and/or windy days, then I have to increase the floor temperature up to around 38 degrees.
Acuario
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You say the floor is typically 31 to 34 and needs increasing for exceptional weather, is your controller allowing for outside temperature (weather compensation) or just working at a fixed temperature?

Our ongoing project (underfloor heating across 3 floors, ground floor in screed and aluminium spreader plates upstairs) maintains indoor temperature within 1 to 1.5C (in winter) by automatically adjusting the water temperature based on outside temperature.
The lag in our system is significant, if i were to let room temp drop to 18c, it would probably be 2 days before the house was back to a stable 20.5.

At +10C outside we need 23C water and at -5C outside we need 28C in the floor.
The actual surface of the floor doesn't really move from 23C so i think it's more about the the amount of watts pumped into the floor than the water temperature itself.
Eventually we will have internal room thermostats to tweak individual room temperatures.
The only time the system struggles is spring and autumn when chilly nights demand heat into the floor and warmer sunny days cause overheating with high solar gain onto an already warm floor.
Being able to predict a warm day ahead would help our system, predicting colder weather less so.

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Old 02-02-17, 06:20 AM   #7
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It sounds like we are following similar paths. I don't think the lag is quite as significant in my system as yours but it is certainly measured in hours.

What I have at the moment is simple, it aims to maintain the floor water temperature at a set value but, as you rightly say, this doesn't maintain the room temperature. So far I have been manually altering the water temperature depending on the weather.

The whole idea of the enhancement I'm working on now is to use the predicted future temperature to increase or decrease the water temperature early to compensate for the lag.

As the house is occupied 24 x 7 I'm not worried about controlling daytime/weekend temperature changes although I may do something about reducing the night-time temperature a degree or two.

I've only just started recording values for outside/inside/water temperatures to plug into my equations, I think we have pretty similar figures which is encouraging, for example 9C outside, 30C water => 23C inside.

The weather feed I'm using gives 3 hourly predictions for 5 days ahead so you could use that to feed into your system.

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Old 02-04-17, 01:01 PM   #8
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As you are now measuring inside, outside and water temperature you have all the inputs you need for a simple automated weather compensation.
That may well be close enough that you don't notice any lag.

I could probably make our house recover quicker from a temp setback by raising the floor temperature much higher for a couple of hours then dropping it as the room temp recovered. My feeling is the tiny bit of energy saved by lowering the temp at night would be dwarfed by the loss in heatpump efficiency when running at elevated temps.

The idea of a predictive element in equation sounds great, just not sure as i want my heating system online, or to need to be online to work correctly.

Currently running Codesys on a raspberry pi with arduino mega's as I/O nodes over modbus tcp.

When i catch up on my jobs/project list i will have a go at reading weather forcasts to see how accurate/useful it is.

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Old 02-09-17, 06:26 AM   #9
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The predictive weather input idea could also be a real boost to heat/cool systems with some heat storage capability and particularly with the option of using alternate heat sources such as solar water panels coupled with a geo heat pump, as does Actuario.
If you knew you had cold cloudy weather coming , you'd know (or your system would know!), you'd start using your geo hp system to start storing heat in your storage tank ahead of the cold weather as well as ramping up your hydrionic floor (if you had that)
But if you knew cold but sunny weather was coming, you would forgo the hp for storage because you'd be able to rely on thd free solar input.
And dozens of variations in between and added variations like predicted wind speeds as well.
Coupling predictive weather with some storage might allow you to go with a smaller system and save some kilowatts in the hp system overall.
But the software would be compplex. Someone must have done this in big commercial systems like high rise buildings?
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Old 02-09-17, 06:59 AM   #10
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This guy did something similar. He hasn't been active in a while

https://frugaltinker.com

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