http://uk.farnell.com/jsp/Industrial+Controls+&+Automation/Humidity+&+Rain/HONEYWELL+S&C/HIH-4000-001/displayProduct.jsp?sku=1187547&_requestid=78603

From Farnell, "HIH-4000-001 — HONEYWELL S&C — HUMIDITY SENSOR, 2.54MM SIP", Farnell order code 1187547

Used to detect that someone's having a shower, etc.

When paired with the float sensor in the loo, covers both reasons why you'd switch the fan on! Use a dwell-of on the float sensor, and switch the fan off when the humidity is acceptibly low.

Needs 5v supply, and delivers 1-4v output to be connected to analog input

-- Alistair

 Here's some important notes:

  The location of the HIH series is very important, if you place these too close to the show cubicle then water will condense on them and it'll be hours before you get a sensible reading.

  If you can, a good two meters from the shower is good, and if possible here a source of gentle heat.

  The reaction to a shower starting is very quick I've observed less than 10 seconds at 1m from the shower.  Typical reading are around 60-75% for a dry room (as seen by the Analogue inputs, actual RH lower).  Whilst a shower is running, 100% which would indicate that the output is closer to 5V rather than 4V as stated in the datasheet.

  In configuration terms I have mine set using thresholds, above 99% -- ON chan FAN below 99% OFF chan FAN.  This is because this sensor sees rising humidity much faster than falling humidity.
 

Theory is the sensor outputs anominal signal of 1 to 4V, graphs show just under 1V at 0 RH and 3.75V at 90% RH. The webbrick input is 0 to 5V, this is mapped onto the range 0 to 100%. Therefore at 0% the webbrick input is circa 1V and the UI will display 20%, At 100% the input is nominally 4V and the UI will display 80%. The webbrick gateway has the ability to scale these values to map them back, but best to let the webrick switch the fans.

The other observation is that RH will go back up when the fan switches off, probably due to the air flow over the sensor being ok and when the fan stops more mositure evaporating off the walls and floor.

The location  can be problematical, I have seen one installed around a corner from the shower itself and away from fan outlet, so there is a bit of a dead spot in the air flow, It may be best to use the sensor to trigger the fan and then run the fan for at least 30 minutes using a dwell. The low threshold could be set to switch off sooner is the RH drops fast.

 In terms of placement.  We found that they are also light sensitive, with a 3-5% higher reading with the lights on. (WB 6.3 night time)

 In terms of runtime, we found that 5 mins was sufficient to clear a fully steamy bathroom (3m x 3.5m).  This of course depends on the fan used.  For our test application we'll be replacing the fan with a larger model, removing the control circuit and using a spare channel on the dimmer pack to reduce the speed and thus the noise levels.

So I’m thinking about adding a tiny silent 5V fan, which’d always blow the air onto the sensor, and thus evaporate anything which would have condensed, and putting both the sensor and fan in a small grilled box.

Any recommendation about a suitable 5v fan to use? -- thanks

Why not use the fan you already have in place?  Position the sensor at the extract fan room outake so that the extract draws air over the humidistat evaporating any condensed moisture quickly and ensuring a representative sample of actual RH as the dry make up air is drawn into the room. 

Alternatively, if not using central extract,  many commercial units eg. Airflow Icon http://www.iconfan.co.uk/ have modular detectors which are ideally placed in the fan casing - choose a LV version and lead it out to the Webrick!

However you achieve switching, careful placing of the fan is important as well  - you need to ensure that the fan is positioned away from the source of makeup air so that air flow does not 'short circuit'. The fan needs to make sure air flow moves throughout the room otherwise it will not change all the air and RH will not drop effectively - result - mouldy bathroom 

Simon

 Simon,

Fair Play!  this is exactly what we did, its been running this way for two weeks now.

However you've beat us to it.  In our case the fan inlet is directly above the shower cubicle and the start-up is within seconds.

The run-on is suprisingly short, at about 30 seconds, however this is not the end of the story. It generally starts up for a minute or two after about 5 minutes and will make some short runs in the hour or so after the shower has been used.

For us this is pretty acceptable since it minimises the warm air (energy!) lost from the room.

However the main reason for delaying the 'reveal' of results is that the data sheet for the Honeywell sensors state they should be used in a non-condensing enviroment. I've been wondering if there would be any corrosion on the sensor surface that would change the characteristics.

I'll report to this thread if the results change.

 Regards

Andy
 

Andy,

A few more thoughts on the subject for everybody.

You're happy with this situation for heat conservation - however time may tell a sorry story for the grout and silicones in the room (as well as, possibly, the transducer)particularly in Alastairs place where heating is likely to set back for extended periods and then the lower dew point will leave more free water sitting about for a while

IMO your 'issues' stem from two reasons:

First - the speed of response of the transducer is too quick and is therefore reading 'transducer local' conditions and switching the extract off too soon. the RH then reequilibrates in the room and the system switches in again. This situation repeats  until RH equilibrates below threshold - classic underdamped analouge control loop!!

Options - to keep the fast response time you need to apply some integral action to reduce overshoot.  The simpler option is to reduce the proportional action.  Probably both a s part of a tuning exercise (Andy, remember Zeiger Nichols? and the ridiculously over sensitive adjustments on Kent controllers, bellowes pumping till they popped :-)

Neither easy to do properly in the brick itself, so necesitating external circuitry followed by tuning - a amusing divertion for those of us with too much time:-) to make a living just buy a humidistat where all this work is largely done for you.

Alternatively apply a much larger switching hysteresis to the system ie fan overrun via dwell as Lawrenece suggested earlier.

Analogue instruments interfaced with digital actuators are often problematical in terms of loop stability - the digital action introduces 'high frequency' harmonics into the loop which can destabilise the same way as any high bandwith feedback loop cf the need for low pass debonce filters on the brick DI

Another approach to taming this may be to use a speed controlled fan that ramps down with decreasing humidity. This would give yo several other possible benefits interms of setback speeds at night etc.  I think Justin Mackey is doing something along these lines - not sure if he is controlling on humidity though, Justin?

The second issue - the condensing.  The sub kennel sized British bathroom is never going to be anything other than a 'condesing environment'  without blowing a noisy, energy consuming gale through, while webbrick builds are quite likely to be in larger properties, any gains in siting possibilities are likely to be offset by the probable lowering in effectivness of extract.  While keeping the transducer in the airflow is one method of controlling condensation it is at odds with achieving fast acting tight band control.

IMO any encasing/heating/wafting etc is really only reproducing a commercially available stat, at which point one has to ask if the bare transducer is suitable.

In ducted fans/centralised systems one could use an in room transducer for fast switch on and a downstream sensor to switch off - this is just another way of increasing switching hysteresis albeit with greater level of band control than a one size fits all dwell.

The all time best solution I've ever found to humidity in the bath room - open the window:-) ......now what sort of actuator........

I'm gonna stop now as I sense I have probably drifted some way past OT

Cheers

Simon

Off topic, No. I like window open approach. But issue is a lot of the larger houses the 'Ensuite' bathroom still does not have a window. Actuator, I think two stage issue, some of the larger servos would do - see AndyH doors over webbrick. But then security and I think you would end up with a solenoid lock so window secure. There again fanlight windows simple bit of wrought Iron as a posh grill so when open no access and a servo to control the opening.

 Hi Everyone,

 This is my first post, so I'd like to say hello officially.  I've been reading through this post and for what its worth...would it be good to use a flow sensor in the shower feed to switch on heating thus raising the ambient and reducing the tendancy for condensation?  A humidistat-fan combination could be used as well, and putting in a certain amount of histeresis (as in room 'stats) would be a really good idea.

Anyway, just a thought......

Andy
 

Another good idea.

Main issues are building regs: My understanding is that if the bathroom has a window that opens then you need a Fan, if it has no windows then you need an automatic fan controlled by a humidity stat or is a fan switched by the lights with a set runtime enough to comply with building regs.

Otherwise a flow sensor to up the heating could help but you still need top vent the damp air.

Ah yes, the Building Regs.  The full explanation is given in Approved Document or Part F & F1 on the DCLG website which you can download for free.  Paragraphs 0.16 to 0.19 gives guidance on automatic ventilation.  Paragraph 1.5 in F1 states that you need ventilation in kitchens, utility rooms, bathrooms and sanitary accommodation.  Table 1.1 gives the values for each location and a few other bits of information.  The extract rate for bathrooms is 15litres / sec for intermittent extraction in a bathroom (which is what we're talking about) and 6litres / sec in sanitary accommodation. 

 I couldn't find a reference to opening windows and the effect that has upon the extract rate.  I don't want to say that it is a myth because I have a feeling it does have a bearing on the extract rate requirements; but there was no mention of it as a footnote to the table or in the text eg. "...or 10l a second where an opening window of..."

 
On a slightly different note, is there a forum for building regs on the site and does anyone else think it would be useful, or is it best to discuss that sort of thing in a thread so it stays relevant?
 

Andy 

4 parts to ventilation requirements

Extract moisture

Dilute and remove pollutants

Background ventilation

Combustion requirements

We are discussing fans to dilute and remove pollutants and extract moisture - this is a requirement in a bathroom or sanitary accomadation with or without a window

A window and/or trickle vent will provide background ventilation(according to the regs) and may in some rooms provide the dilution of pollutants where its openable area is at least one twentieth of floor area!!

In a bathroom with no window the fan must run on for 15 minutes and a 10mm air gap must be allowed under the door, or equivalent air source, to substitute background ventilation.

I mention opening the window because in my experience their is no substitute for quick air changes in any room, however the number of people who seem  not even to entertain the idea is not small:-)

Any mechanical extract must take account of its effect on an open flued fuel burning appliances (or fireplaces) as the effects of sucking combustion products back into the house are lethal.  CORGI, in particular, have a shiny new initiative on this subject and the powers that be will not be sympathetic to transgressors!!! 

Of course whilst part F wants a healthy draft through part L wants the place sealed up tighter than the proverbial :-)

Simon

Simon,

thanks for taking the time to put that "in a nutshell".  I think that we can safely say that the left hand wrote Part F and the right hand wrote Part L.  Guess we all have to use whole house ventilation and heat recovery.  Now, did someone say they had a box of tricks that could control that?

PS what is one twelfth of the total floorspace of a nutshell? 

Andy,

One of many nuts one would have to squirrel away to cover even the domestic subject!! 

The approved documents are  often not easy to follow as they are not really arranged in a manner to examine all subjects pertainning to, say bathrooms, in one place - there are quite a number of BR interpretation/application books out there which I find very helpful to check out all the oft conflicting requirements.  This one is pretty good if you want to keep to a sensible price  - due an update but read in conjunction with the AD on the web..... http://www.amazon.co.uk/Building-Acts-Regulations-Applied-Houses/dp/0582432154/ref=pd_bbs_sr_1/026-9161195-1859642?ie=UTF8&s=books&qid=1193089506&sr=8-1

I think with the increasing use of heat recovery systems, domestic aircon, ground and air source heat pumps the time is approaching when some enterprising types will pull it all together and start offering domesticly sized air handling units (any one remember warm air central heating??? Kids sniffles all round!! ) for HVAC. Could be pretty useful where circumstances preclude wet UFH? Maybe space too precious in UK?

Now about that box of tricks. Know where I could get one?

Simon