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Old 10-14-14, 08:01 AM   #1
jeff5may
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Default ODR - outdoor reset

What is it and how is it used?

Are there any standard control schemes or algorithms that are commonly used?

I am trying to integrate the control into an arduino sketch.

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Old 10-14-14, 01:19 PM   #2
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Quote:
Originally Posted by jeff5may View Post
What is it and how is it used?

Are there any standard control schemes or algorithms that are commonly used?

I am trying to integrate the control into an arduino sketch.
I'm certainly not the final word on the issue, but here's what I think I know:

ODR's are designed to compensate for the thermal mass of the building + high mass floor if high mass radiant is used.

In a scenario without ODR, the heating system gets its command to begin heating when the indoor temp falls below the minimum set point. If the thermal mass of the house & thermal mass, etc. is very large, the heating system will be in a constant time-lag of overshoot/undershoot.

In a scenario with ODR, the heating system monitors the outdoor temperature as well as indoor temperature, and can "anticipate" the need for heat... thereby eliminating the problem with temperature lag.

Vlad had some kind of uber-smart controller on his hydronic heating system that was able to do ODR functions and also monitor the heat of the thermal storage tank, and with all that information, it would inject controlled pulses of hot water into the circulating water stream, to smoothly maintain optimum temperature.

It had a "learning" function too, that allowed it to learn the thermal mass of the house it was heating.

Cheap Chinese PID controllers also have a learning function built in. The way the learning function works is the controller go "ON" (and start measuring a time interval) until the temperature of the water, as an example, reaches the set point, then they turn "OFF" (and start measuring this time interval), and wait until the measured temperature returns from overshoot, and hits the set point again. So, by just knowing the time it takes to reach a set point, and the time to return from overshoot, back to the set point, the effective thermal mass can be calculated.

There are PID routines available for the Arduino... maybe even learning routines also, so you won't have to re-invent the entire wheel.

This might help, too:

http://tekmarcontrols.com/solutions/...y-savings.html

I don't think that ODR's are needed if the house + heating system is low mass, or if severe sudden temperature changes are not an issue.

Good Luck.

-AC
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Old 10-14-14, 02:50 PM   #3
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Assuming outdoor reset is the same as what we what we call weather compensation in Europe, the main function is to adjust the temperature setpoint of the heatpump based on the outside temperature.

As the outside temperature drops the required flow temp to heat emitters rises. Set correctly you can have a reasonably consistent inside temp without a thermostat.

Extract from Worcester Bosch heat pump technical info.


The above functionality can mostly be achieved with this code.

Code:
  float ost;

  ost = 20 - Outside;
  WCtarget = ((WCcurve * 0.16 * ost) + 20);
  WCtarget += WCofset;
Outside is the measured outside temp
WCcurve is the chosen heat curve (0.1 to 10, try 3 for underfloor heating, 5 for radiators)

WCofset is the chosen ofset (-10 to + 10)

WCtarget is the output of the equation and therefore the target temp for the heat pump.

Whilst this code works fine it takes a lot of tinkering with to get the exact settings for YOUR HOUSE.

Simpler code, simpler setup for the same result.(I've not tested this but see no reason why it won't work)
Code:
DesiredWaterTemp = map(osTemp, coldOS, hotOS, coldWater, hotWater);
osTemp it the current outside temp

coldOS is the outside temp on a cold day, you need to record this value and the required water return temp needed to heat your house.
coldWater is the return water temp you recorded on the above cold day

hotOS is the outside temp on a warm day (that still requires heating), you need to record this value and the required water return temp needed to heat your house.
hotWater is the return water temp you recorded on the above hot day


DesiredWaterTemp is the flow/target temp from your heat emitter or buffer tank.

Hope this helps

Steve
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Old 10-14-14, 06:29 PM   #4
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OK, so I found a page that describes outdoor temperature reset pretty well:

http://www.comfort-calc.net/Outdoor_Reset_Info.html
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Old 10-14-14, 07:30 PM   #5
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yes, weather compensation is the same as ODR. All new condensing boilers come with it or the thermister is an option.

They do not, as a rule, measure the indoor temps but it is an option to do it. I have a Viessmann boiler with ODR control and no internal t-stat. The wife hates it but it always maintains the desired temp in the house. Mine has setback schedules as well but I don't use them with high mass radiant.

The first company on this side of the pond to really do anything with them is Tekmar and they still the leader in resi aftermarket controls.

My control on the boiler is set to raise up 0.8C for every 1C drop in outdoor temp (typical starting at 20c but I start it at 16C outdoor temp.)

I've been putting them in for 20+ years.
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Old 10-18-14, 07:37 AM   #6
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My (NIBE) heat pump uses this approach and it works well for keeping the temperature constant as the weather changes, but it doesn't seem well-suited for situations where the house must be brought up to temperature from cold. Say after a power outage, or after a temperature setback period. It seems that the heat pump adds enough heat to offset the losses to the outside, but doesn't add any/enough to raise the temperature.
Not a problem for us as we keep the temperature steady, but if you wanted to vary the temperature significantly this may need some override based on the internal temperature.
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Old 10-18-14, 08:02 AM   #7
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Which is why I don't recommend using a night setback with a heat pump. They are not like a gas boiler with lots of reserve heat available.
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Old 10-18-14, 11:48 AM   #8
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Quote:
Originally Posted by Mikesolar View Post
Which is why I don't recommend using a night setback with a heat pump. They are not like a gas boiler with lots of reserve heat available.

Mikesolar,

Are you stating this as applying to ALL heat pump situations (mini-splits are heat pumps, too) or are you referring to high-mass radiating systems?

Reason being, I am currently using an ASHP to heat my house, 9,000 BTU mini-split, with a built-in set back feature, and there is no problem what so ever.

-AC
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Old 10-18-14, 02:56 PM   #9
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Quote:
Originally Posted by SDMCF View Post
My (NIBE) heat pump uses this approach and it works well for keeping the temperature constant as the weather changes, but it doesn't seem well-suited for situations where the house must be brought up to temperature from cold. Say after a power outage, or after a temperature setback period. It seems that the heat pump adds enough heat to offset the losses to the outside, but doesn't add any/enough to raise the temperature.
Not a problem for us as we keep the temperature steady, but if you wanted to vary the temperature significantly this may need some override based on the internal temperature.
This is OK with me for the types of control the way the controller I am planning to do will use the out door sensors. This outdoor control will work with a heat pump that is refrigerant based. My question is this:

How well do these controls save energy when rigged to a gshp or ashp for outdoor heat gathering and a water cylinder for a heat dump? I understand that with gas burners, less gas corresponds directly to energy and cost savings. With phase change devices, the calculations are not so simple or direct.

For simplicity sake, assume two situations:

1. Retrofit or integrated into a boiler or dhw loop where design day temp is around 130degF.

2. New or integrated into hydronic loop with design day temp below 100 degF.

Last edited by jeff5may; 10-18-14 at 03:05 PM..
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Old 10-18-14, 03:34 PM   #10
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Quote:
Originally Posted by jeff5may View Post
This is OK with me for the types of control the way the controller I am planning to do will use the out door sensors. This outdoor control will work with a heat pump that is refrigerant based. My question is this:

How well do these controls save energy when rigged to a gshp or ashp for outdoor heat gathering and a water cylinder for a heat dump? I understand that with gas burners, less gas corresponds directly to energy and cost savings. With phase change devices, the calculations are not so simple or direct.

For simplicity sake, assume two situations:

1. Retrofit or integrated into a boiler or dhw loop where design day temp is around 130degF.

2. New or integrated into hydronic loop with design day temp below 100 degF.
For dhw heating the odr needs to be disabled as it would limit water temp.

For hydronic heating purposes the odr limits water temp to just hot enough to keep the house warm.
It saves energy due to the way refrigerant heat pumps power consumption is proportional to the output temp(and to a lesser extent the input temp). The higher the output temp the higher the power consumption.
My ASHP draws around 850w when heating my floor to 24C and 1300+w when heating my water tank to 50C.

Steve

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