HVAC - Trying to get a better understanding

[Nad]

Hi all,

It seems to be rather quiet round here these days, i'm sure i saw some tumble weed!

Any way, I've finally been getting some time to play with the HVAC object and have been seeing some odd behaviour compared to what the help files should say happen. So i was hoping someone could clarify exactly what the behaviour should be for the following.

1. HVAC Override: It should change the heating profile used to the occupied profile and then once the temp reaches the set point temp the override should be removed?

2. Heating Increase Temp: The temp should be raised by 0.5C from current room temp and then once the room temp reaches the new required temp the heating goes back to the pre programmed profile?

Thanks.
Nad

[toscal]

the only problem here is that once you either do your override or the increase, as soon as it has reached the temp it then goes back to normal. In my opinion not good. If its really cold then you may have to do it again. Not a problem if it once but what about three or four times.
Why not have a heating boost function, that you can say once new temp has been reached maintain for 20 minutes or 30 minutes, Or have temp boost 30 mins and temp boots for 60mins.
I think 0.5C is not enough, most people won't notice a half degree drop needs to be whole degrees.
Occupied and unoccupied. I've done this with an x10 system. Basically the heating is programmed like this
Weekdays
ON 07.30 Off 08:45
ON 16:00 Off 22:00
Weekends
ON 07:45 Off 09:00
On 16:00 Off 23:00
heating on temp is 22C off temp is 15C
Then we did when house is empty use 17C when heating is on. The when house is occupied set ON temp to 22C
Works quite well.

[Gumby]

The increase temp should hold until the next point in time that the demand temperature profile changes up or down - not when the room hits the demand profile.

In essence, this is a boost function, but rather than run for a fixed time period it assumes that the shape of the temp demand profile represents key times in the occupier's day.

The occupancy override is a bit like a "pre-heat" - if you were in the room then it would be heating to the occupied profile anyway. So this override only makes sense when you are expecting to not be in the room. I suppose this is a little bit like "advance" controls on time clocks.

Ideally there should be little need for boosts. The system features configurable outside temperature compensation for each HVAC object (ie every zone) to handle extreme weather. But sometimes people can feel cold despite the room temperature being as demanded. That's the point I tell my wife to put another jumper on

At the point that these controls are not sufficient I'd say you'd be looking at your demand profiles or temp compensation and seeing whether they need tweaking.

[Nad]

Thanks for the quick response guys

At the moment I have a occupied profile set at 20C between 07:00 and 23:00 and then 18C between 23:00 and 07:00. The unoccupied profile set at 17C at all times.

This setup works really well and to be honest there is no need for us to use the temp increase function.

But ...

I just wanted to make the temp increase option availabe for the wife via the DFP. For some reason this is not behaving quite as expected. The temp increase is increasing the set point even though the menu stated temp increase. In addition, it's increasing the set point for both occupied and unoccupied profiles.



On the topic of HVAC override.

Just like Gumby said, I use it as a pre heat for before we get home. We don't have a fixed routine so some times we are home early, some times late and some times not at all. So I send the override command via email an hour or so before we get home. All in all this also works very well (when we remember to send the email ) but the override status remains active till I resend the override command or manually take the override off. So if i forget to take the override off the house remains at the occupied profile even when no one is at home.

Hence why I asked for the clarification of the funtions ... trying to get a better understanding of what's going on

Thanks.
Nad

[Karam]

As Gumby suggests, the override is to temporarily override the unoccupied status until the temperature reaches the (occupied) setpoint at which point if the occupancy state is still zero then the override should be automatically released. You can perhaps look back at your data for an occasion when you used the override in this way and see whether the occupancy state was indeed zero at the point at which the temperature first reached the occupied profile. Or you can send us the history file and database for that day and we can analyse.

The increase/decrease temperature feature has even more subtleties than most people would imagine . If we first start by defing 'setting' as meaning the target temperature (or set point), then we had a long running debate in the early days as to whether one should increase the setting relative to the presently measured temperature or relative to the present setting. In the end we provided both options. However either option will cause a temporary change relative to the usual profile. As Gumby pointed out this change is removed when the next change in the profile is encountered.

With the availability of hour resolution profiles people tend to eventually move away from say a couple of settings during each day to more variable shapes, so typically profile changes tend to happen a bit more frequently than in your case. However it should be possible to use a more traditional method such as a macro in order to remove the change in an arbitrary period of time.

The 0.5C step is just what we have considered to be the minimum discernable temperature change. Given the dynamics of heating systems and the desire to be as gentle as possible with energy usage a small step size was chosen. It is not uncommon for people to believe that increasing the setting by more degrees will speed up the heating process but in the majority of heating systems this is not the case. You can however simply press the designated boost button a couple or more times in succession to multiply this up if required. Obviously you can also get feedback on the new settings either by speech or on the LCD. You can also program other forms of feedback if you like - for example an LED indicating heating demand state is useful visual feedback at a distance - to tell you that the system is actually still heating up towards the set point, so negating the urge to apply a boost (or further boost)

[Viv]

Hi Nad,

It looks like you are constructing an HVAC menu yourself which is OK.
Just incase you are not aware, the HVAC has an input typically connected to a button called 'Configure and Activate Menu'. This will cause the HVAC to automatically build the HVAC menu for you and then start it. From a users point of view it simple starts the HVAC menu. However it does allow access to HVAC's in other zones that the one you are in. Usefull if other rooms do not have control panels. However you may consider it offers to many options and therefore constructing one yourself if preferable.

Viv.

[Nad]

Viv/ Karam,

I've made my own menue simply becasue i wanted to keep it as simple as possible. So if my wife feels cold then she goes to the pannel and increases the temperature without having to figure out what all the other functions are

In general this works really well and besides a couple of little quirks it works fine.

Quirk 1: When you press the increase button for the 1st time the DFP shows/ announces that the temperature is set to fall by 0.x degrees. So if the set point is 20 and the current temp is 20.3 then i get the message that the temp will fall by 0.3 deg but the DFP (i have set point and actual temp shown on the DFP) shows the new set point to be 20.8.

Quirk 2: The temp increase changes the set point (as it should) but then the change in profile doesn't change it back to the default setting unless i execute the return to normal function.

With regards to the Override function, what would happen if the room is in override mode and becomes occupied before the occupied profile temp is reached? So I tell cortex via email to set the override on which should bring the temp up to 20 deg, it's 17 deg at the moment, but we get home and enter the room so it is now occupied but the temp is 19 deg. Could this be causing cortex to get a little confused?

I'm considering writing macros to reset these functions, but just thought i would ask first

[Viv]

[QUOTE
Quirk 1: When you press the increase button for the 1st time the DFP shows/ announces that the temperature is set to fall by 0.x degrees. So if the set point is 20 and the current temp is 20.3 then i get the message that the temp will fall by 0.3 deg but the DFP (i have set point and actual temp shown on the DFP) shows the new set point to be 20.8.
]

When you press the increase button the first time you do get a report rather than an action. The rational being that if it is cold in the room, and it is heating then asking it to heat more is probably not what is required but simply to allow it to continue to heat the room and get up to temperature. Similarly if it is already above the setpoint then it informs you by reporting that currently it is allowing it to fall. I must say I am not to comfortable about this first report behaviour. Perhaps others have an opinion?

The setpoint report showing the wrong value must be a bug and I need to investigate.

[QUOTE..
Quirk 2: The temp increase changes the set point (as it should) but then the change in profile doesn't change it back to the default setting unless i execute the return to normal function.
]

Let us say the setpoint is 20C. You have asked it to raise the temp to 23C. So an offset of 3C. The next hour says Setpoint is 21C. The offset is now changed to 2C in otherwords it still targets to 23C. The rational is that if normally the target is 20C and that was not good enough that you asked for 23C then in the next hour 21C will still not be good enough.
However if the profile drops to say 18C it suggests by implication that the room need not be as warm at the previous hour at 20C and the likelyhood is that the room will not normally be occupied at which point the offset is cleared to 0C.


[Quote...
With regards to the Override function, what would happen if the room is in override mode and becomes occupied before the occupied profile temp is reached? So I tell cortex via email to set the override on which should bring the temp up to 20 deg, it's 17 deg at the moment, but we get home and enter the room so it is now occupied but the temp is 19 deg. Could this be causing cortex to get a little confused?
]

The presence override is internally a separate state. The occupied profile is used if the room input informs it is occupied or if the run-on period is active or the presence override state is true. Therefore setting the presence override and then the room becoming really occupied should have no effect i.e. the presence profile should still be used.

The presence override state is automatically cleared when the rooms internal temperature exceeds the occupied demand temperature. The occupied demand temperature is the occupied profile + the outside modifier + the user offset. The outside modifer is the setpoint offset based upon outside temperature. The user offset is as described previously.

Viv.

[Viv]

Updates have been made to Cortex 24.
On first request for increase temperature, if it is already heating then it reports the status.
On first request for decrease temperature, if it is already off then it reports the status.
If above are not satisfied then it performs increase or decrease.
On second press (within 30 seconds of first press) then it performs increase or decrease.
Spoken report of action and status gives more information e.g. 'heating has now turned on' (if applicable).
Return to Normal operation now gives more status information.

Presence override auto clear only worked for HVAC mode = automatic e.g. heating and cooling. Now works for mode <> off.
Status display on DFP LCD should now sync with action and provides more information.

Viv.

[Nad]

Updates have been made to Cortex 24.
On first request for increase temperature, if it is already heating then it reports the status.
On first request for decrease temperature, if it is already off then it reports the status.
If above are not satisfied then it performs increase or decrease.
On second press (within 30 seconds of first press) then it performs increase or decrease.
Spoken report of action and status gives more information e.g. 'heating has now turned on' (if applicable).
Return to Normal operation now gives more status information.

Presence override auto clear only worked for HVAC mode = automatic e.g. heating and cooling. Now works for mode <> off.
Status display on DFP LCD should now sync with action and provides more information.

Viv.

Viv,

That's awsome
Gives me something interesting to do when i get in today, i assume 24.4.1 is available to download?
On a side note ... did the google mail connector manage to make it in

Thanks,
Nad