temperature and humidity control for ventilation

[Richard]

I am interested in providing a monitoring and control of home ventilation "fresh air" based on humidity, temperature conditions.

Using outdoor air, to vent and dehumidify an interior space when conditions allow
sucessfull removal of indoor humidity.

For example a final device is "ON" for 30 minutes

if the humidity
indoors > 60 % and temp is > 65 deg.

AND

Outdoor humidity < 80 and temp is < 70 deg.

Additional condition can be added to HS events for the trigger.

Is this accomplished with the current mcs Controls ?

and probably more important can I achieve ventilation and humidity reduction if I integrate a humidty & temp rule process such as this ?

Seems to me to be a really great environment control. I could gain fresh air when conditions are favorable.

A smart "open window".

Thanks in advance
Richard

[Michael McSharry]

You have four independent and one dependent variable in your equation so direct control of this specific algorithm from the GUI may not be possible or awkward if possible.

From the parameters you described I could not tell what objective you are trying to achieve, but a fan on for 30 minutes will achieve the objective when the conditions do exist.

The general concept behind the plugin's trigger and actions control are to support a closed loop control system. When you indicate that you want a fan on for 30 minutes you are implying an open loop control and this type of control can just as easily be achieved with the native homeseer trigges and events.

I assume you are trying to get the inside to feel like the outside when the outside conditions are within a certain comfort zone.

If this assumption is the case, then you first need to define what "comfort" means in terms of humidity and temperature. You may find that for this applicatioin that these two are independent.

For example, assume that humidity have equal temperature have equal importance and their range is roughly the same. The product of the two could then be the comfort parameter. Now you are comparing the inside comfort vs the outside comfort and turning a fan on when the delta between the two is outside a hysterises band. Note that "Time" is not part of this control. The fan will stay on exactly as long as is needed to transfer the comfort level from the outside to the inside. If you make the hysteresis band small then the fan will cycle often. If you make it large then it will stay on and off for longer periods.

In the context of the plugin's trigger control you need to have two virtual devices that are computed in a script periodically. These devices will contain the comfort calculation for the inside and the outside. With these two devices you can then setup a Temperature Control to keep the comfort within the specified upper and lower limits.

You also have other options where humidity and temperature are treated independently. For example, the Temperature Actions event tab can control humidity within a band, but only control it when another device(s) enables it. The other "devices" could be the status of the temperature delta control. The same is done for the temperature control with the humidity status enabling it.

It could all be done directly in scripting to give maximum flexibility, but the essence of the problem is still the same. You first need to determine what you are really trying to control. What does an "open window" really mean in terms of humidity/temperature/ventilation.

[Richard]

Here is the formula for when to ventilate:

Overview

Table 1 is based on a drying rate of four gallons per day and one air change per hour. Ventilation drying using outside air is recommended when the difference between the outside and indoor air's moisture holding capacity is 0.0015 lb H2O/lb DA or greater.

This corresponds approximately to a dew-point temperature difference of 5°F.

When the outside air dew-point temperature is at least 5°F lower than the indoor air dew-point temperature, ventilation air drying is recommended


.....from the other day.
Thanks for the follow-up.

The "open window" really means that I have often by my judgement determined that on certain days when humidity, temperature, and possibly the condition low winds, "the conditions" opened a window to help air the house and provide ventilation for a period.

My judgement includes that when the temp. gets above for example; at 75 degrees and 60 % humidity - close the window due to the outdoor humidity being less comfortable in terms of humidity/temperature/ventilation.

I am trying to turn that type of process into measurable conditions that could ventilate fresh air under the control of HS. & a temp, humidity control process.

That way I could allow HS and its sensors to allow fresh air start for example during periods of reduced temp and humidity to enter my house and when limits of comfort are exceeded the ventilation would stop.

Seems like I am accurate when I say that when outside temp of < 70 and humidity of < 50 % ,this is good time to ventilate.

And it is time to stop ventilating using outside air, when inside air is 72 and 50 % humidity is reached. Maybe then turn on the AC.

So on dry days of moderate temp. a ventilation may occur and stop when conditions change from the range.

Does this simple range of conditions seem to be the key to getting fresh dry air into a home, since mine seems to be rather air tight and humidity levels build up during the spring and fall.

This is when AC dehumification (temps between 50 -70 do not put the AC into operation from a temperature trigger) and if I run AC manually (have to set temp lower) the house gets rather cold with little humidity control actions.

In the north east there are many good days to open the windows for periods of the day, then close them when conditions change in late morning / afternoon on some days.

Richard

[This message was edited by Richard G on Tue, 11 November 2003 at 08:35 PM.]

[Michael McSharry]

I think you are on the right track, but you still need to quantify it in terms of a control solution.

As stated, if it is hot and dry in the house then keep the window closed no matter what it is outside. What about cool and humid inside, but a warm/dry front arrives? What about the morning when it is humid both inside and outside, but you can take advantage of the cool temp outside to cool the house inside?

What I'm trying to get at is you have 4 independent variables so there are many combinations. It is easiest to treat these as independent control functions or to calcualte an objective function based upon the relationship of the two (such as product) that can be controlled. The intuitive answer is easy because the brain does the hard stuff. If you quantify it for the computer, then all bases need to be covered.

When I was living the Northeast I seem to recall that temperature and humidity were usually correlated. If it was hot it was humid. If it was cold it was dry. Control one of these closed-loop and use the other to enable/disable the control loop. Add in another virtual device for manual override.

In your example trigger the control when temperature delta is more than 5 (75 in vs 70 out) degrees and outside temperature decrease to 70 . Temperature Action is fan device on when temperature inside is above 75 and off when inside temp is below 72.

Define a virtual device that represents the humidity factor. The status of this device will be used as conditions for the fan on/off actions. This status may be a function of the delta inside-outside or just a threshold for either. You could control this humidity device from a second Temperature control event if desired.

For example, TemperatureAction to turn this Humidity Device On when outside humidity is under 50% and turn it off when outside humidity is above 70%. In the same event you could define a second humidity device on/off for the inside humidity control band. This/these would be the TurnOn/TurnOff conditions on the first TemperatureAction event.

The above scenario is not intended to be THE ANSWER, but should be reviewed to show one of many approaches to solve this problem with the control loops built into the mcsTemperature plugin. If you want more of a heuristic approach or a combinatorial approach then a scripting solution is likely the easiest.

If the problem can be characterized as a general Ventilation problem then it may be a good candidate for another mcsControlSystems control loop.

[Richard]

I see the overall issues - 4 variables !

I think that the conditions; from Table 1. seem to
work for drying indoor air. Sometimes a electrical dehumidifier is needed, due to indoor and outdoor temps close and the humidity levels not allowing a difference to take place.


Indoor
temp < 70 > 65 deg.
humidity > 60

AND

Outside
temp < 60 deg.
humidity < 70 %

FAN ON for X minutes per cycle.

venting outside to inside will produce a drying effect down to .. the referenced table levels.


From an article on ventilation here was an overview;

Alternative Drying Devices and Principles of Operation

Outside air is not recommended for some combinations of outside weather and indoor air conditions in Table 1. Dehumidifiers, air-conditioners, or desiccant dehumidifiers can be used when these conditions exist.

article on ventilation using outside air.


Example using Table 1: If the outside air is 65°F and 50% relative humidity while the inside air is 70°F and 50% relative humidity, a room dehumidifier is recommended for further drying.

BUT

If the indoor air is at 70°F and 70% relative humidity while outside air is 65°F and 50% relative humidity, outside air ventilation is recommended.

Cold air has a very low moisture-holding capacity. Figure 1 shows how much the moisture holding capacity of cold air increases when it is brought into a house and heated. This increase in moisture-holding capacity enhances drying.

As the outside temperature decreases, outside air ventilation drying always becomes the recommended drying method.

The last line in Table 1 lists the outside air temperature below which ventilation drying is always recommended, irrespective of outside relative humidity. Care must be taken to prevent water pipes from freezing when below freezing outside air is brought into the house.


Overview

Table 1 is based on a drying rate of four gallons per day and one air change per hour. Ventilation drying using outside air is recommended when the difference between the outside and indoor air's moisture holding capacity is 0.0015 lb H2O/lb DA or greater.

This corresponds approximately to a dew-point temperature difference of 5°F.

When the outside air dew-point temperature is at least 5°F lower than the indoor air dew-point temperature, ventilation air drying is recommended.



This system of using HS and a ventilation fan has the ability to achieve results (actually better than) of a $2000.00 + system. Add a HRV "heat recovery ventilator device" and you can transfer indoor heat to outdoor incoming air and improve heating demands further.

HS has the ability to control ventilation and air change rates, humidity, radon fans, attic ventilation in a complete set of conditions and rules.

Overview on air indoor quality

[Richard]

So, if I can measure this I have an operating control system "Houston".

Is this a mcsTemperature reality? Can mcsTemp. do this?

Need

2 humidity sensors indoor and outdoor

1 temperature sensor to measure the range of operation for "dehumidify / ventilation operation"

& and additional points to monitor for condition to start / stop the event trigger. (is it raining, is it windy, ... etc.)

This seems to work in theory.

Thanks in advance



Overview

Table 1 is based on a drying rate of four gallons per day and one air change per hour. Ventilation drying using outside air is recommended when the difference between the outside and indoor air's moisture holding capacity is 0.0015 lb H2O/lb DA or greater.

This corresponds approximately to a dew-point temperature difference of 5°F.

When the outside air dew-point temperature is at least 5°F lower than the indoor air dew-point temperature, ventilation air drying is recommended.


END

[Michael McSharry]

You need inside temperature and humidity. The one-wire is easiest to get this info. You need outside temperature and humidity. If you have a local weather site that you feel is close-enough then you can get this info from the web, or just measure it like you do the inside.

I think I outlined an approach to implementing the control algorithm. If this does not do it adequately, then I'll just put the algorithm into the plugin like the sprinkler controller.