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mata

Member Since: 24 Jan 2014
Location: Manchester
Posts: 148

2009 Defender 110 Puma 2.4 USW Stornoway Grey

Designing a digitally controlled heater system, help needed.

Having been using the defender a bit more recently, and reminding myself how poor the heater control system is compared to modern standards, I've started to design a more modern digital climate control system which would involve swapping out the cable operated diverter valve for an electronically controlled one.

Few of the available electronically controlled valves plumb up in the same way as the defender valve so different hoses are going to be required. What is apparent however is that many other vehicles have the return pipe from the heater matrix permanently connected to the cold side of the cooling system, unlike the defender where the heater control closes the return from the heater matrix as it also closes the input to the heater matrix.

In a previous thread (https://www.defender2.net/forum/topic54969.html) forum member "zsd-puma" addresses exactly this thought, without reply as quoted below.

My question is, are there any reasons anyone can see why the return from the heater matrix could not be plumbed straight into the cold side rather than via the heater control valve giving much more choice of electronically controlled valve?

Thanks in advance, Mat

zsd-puma wrote:
blackwolf wrote:
zsd-puma wrote:
Isn't it basically just an on off valve for the heater with a built in bypass hose? If you fitted a bypass hose between the two pipes that come from engine you can just fit an on/off valve in the feed to the heater and join the returns together.

It's not that simple. With the valve in the cold position, the two engine-side pipes are connected together and the inlet to the heater from the valve (but not the outlet) is shut. In the hot position the internal bypass is shut off and the feed from the engine is conneced to the heater inlet, and the heater outlet is connected to the return to the engine. In effect, the feed from the engine is diverted between the heater inlet and the internal bypass.

Whatever you do with the crappy valve, you still have a poorly designed heater matrix which gets much hotter on the LHS than the RHS.

LR could so easily have got it right with the TDCi heater, but managed again to accomplish a magnificent level of mediocrit, but it does at lest continue the 60-year tradition of unstaisfactory cab heaters!

A lot of other cars simply have a permanently connected bypass, when the heater valve is shut it forces the coolant through the bypass because it can't go anywhere else, when the valve is open it flows through both the bypass and the heater matrix. Given then the heater gets roasting hot the small amount that will go through the bypass when the heater is on shouldn't make much difference.

Just put Tees on the pipes to and from the engine, with a bypass hose joining them together permanently, then joint the flow from the engine to the heater via a valve, and simply plumb the return in permanently to the other remaining pipe.

Here is the flow diagram for a late rover mini for example, i've used it as it's not overly complicated by AC systems. as you can see the bypass is permanently open, it's just the flow to the heater that's switched on and off with the valve. The same principle is used on domestic central heating systems.
The heater wont get quite as hot, but given that it generally gets too hot on a Puma i don't see that being an issue.

Click image to enlarge

19th Dec 2018 12:10pm

hornet

Member Since: 04 Jan 2010
Location: Western Europe
Posts: 321

Whether you work with a permanently open return flow and determine the heating power by throttling the forward flow, or whether you also have a permanent bypass, only makes a difference in the speed at which the heating responds. The original solution is probably only due to the simplicity of the solution or the value for money of the component.
Your idea is good!

19th Dec 2018 2:46pm

mata

Member Since: 24 Jan 2014
Location: Manchester
Posts: 148

I’ve found a four pipe valve that should be suitable and have written some code to control it. Should be able to test a proof of concept using a heat setting of 1 to 10 before I get any further down the road of proper automated climate control.

23rd Dec 2018 8:41pm

dantastic

Member Since: 04 May 2010
Location: London
Posts: 367

I'm really interested in this project. Like yourself I find the heater controls nothing but stupid.
Is this also going to interface with the A/C?

24th Dec 2018 9:53am

mata

Member Since: 24 Jan 2014
Location: Manchester
Posts: 148

It absolutely could control the AC, although cars I’ve driven that have auto climate as standard have all had AC control on a seperate button.

Once the valve is installed with manual cnntrol working I’ll be moving on to automatic temperature control, which might require more complex code than a simple thermostat due to the sudden variance in coolant temperature with engine work, plus the large / slow reacting thermal mass of the inside of the vehicle. When that’s working satisfactorily I’ll be looking at fan control and hepe to be able to program a ‘half’ setting as, in my opinion, position one on the standard system is too fast / loud.

24th Dec 2018 10:37am

dantastic

Member Since: 04 May 2010
Location: London
Posts: 367

I suppose the A/C always work on a separate button, as you say.
Even having better manual control would be a massive improvement. Better fan control would me amazing as well.

Although I'm a programmer by day I wouldn't be working with this type of stuff so this is a very cool project to me.
I'm a mobile developer so I'm scratching my head trying to think how I could be of use! 😂

24th Dec 2018 11:02am

B4Lamb

Member Since: 21 Mar 2015
Location: Abergavenny, Wales
Posts: 233

2007 Defender 90 Puma 2.4 HT Galway Green

mata wrote:
I’ve found a four pipe valve that should be suitable and have written some code to control it. Should be able to test a proof of concept using a heat setting of 1 to 10 before I get any further down the road of proper automated climate control.

does the valve you have found operate with a servo motor or stepper motor, or just a simple solenoid?
what microcontroller are you planning to use and are you going to use full PID control? "You are never to old to learn something new"

26th Dec 2018 9:07pm

mata

Member Since: 24 Jan 2014
Location: Manchester
Posts: 148

Soleniod.

Using an Arduino, will decide weather to go with PID depending upon how successfully it works without it, to begin with.

26th Dec 2018 9:12pm

B4Lamb

Member Since: 21 Mar 2015
Location: Abergavenny, Wales
Posts: 233

Yes good idea but maybe some differential on top of proportional will be required to prevent overshoot. Have you managed to characterize the valve (current drive vs aperture opening or flow rate) ? I'm interested in your project success and wish you well. "You are never to old to learn something new"

26th Dec 2018 11:29pm

mata

Member Since: 24 Jan 2014
Location: Manchester
Posts: 148

The valve is either open or closed, control is implemented via PWM at 0.3 ish Hz. So far I’ve written some code to control the PWM with ten presets from 0 to 9, I plan to test witha bit of real world driving / use before getting into automatic control and PID.

26th Dec 2018 11:47pm

B4Lamb

Member Since: 21 Mar 2015
Location: Abergavenny, Wales
Posts: 233

ok, I get it. I'm assuming he valve is designed to be controlled like that and not wear out by constantly shuttling every 3 seconds. How does the factory fitted valve work that's connected to the temperature rotary knob? Is that a proportional valve and did you consider just driving that with a servo or stepper motor and gearbox to get the required torque? "You are never to old to learn something new"

27th Dec 2018 12:03am

mata

Member Since: 24 Jan 2014
Location: Manchester
Posts: 148

Yhat’s how it’s meant to be controlled.

I considered hijacking the existing cable operated valve but many have had reliability issues with them and mine is quite vague anyway. I’m aiming for an OEM standard finish and didn’t feel stepper motors / gearboxes/ linkages, potentially under the bonnet with associated heat cycles etc would give me that. This valve is one moving part and is a proven device and method of control.

27th Dec 2018 8:06am

B4Lamb

Member Since: 21 Mar 2015
Location: Abergavenny, Wales
Posts: 233

Okay good point. The temperature control in my TDCI seems to be quite linear but it's hard to get a cab temperature that is right. It certainly shuts completely off and opens completely on which is no different from your digital solenoid valve but there is a usable gradient between the two extremes that potentially could be used in a linear feedback control loop. Anyway good luck with your approach, it sounds like it will be effective with minimal moving parts. "You are never to old to learn something new"

27th Dec 2018 9:38am

edo

Member Since: 20 Aug 2018
Location: Surrey
Posts: 358

Likewise the heater is staggeringly

. Even off it chucks out heat, and having the AC button on but fan in off, still runs the system??

27th Dec 2018 1:24pm

B4Lamb

Member Since: 21 Mar 2015
Location: Abergavenny, Wales
Posts: 233

Just did a test of the standard heater system in my 2007 Defender 90 Hardback.
Conditions:
Start: Engine cold at ambient Ext Temp - approx. +10 C
Heater turned to full on HOT
External Air Intake
Fan setting 1
Setting: Windscreen + Legs
Ch1, External Air Temp (Blue)
Ch2 Heater O/P Legs - drivers side (Red)
Ch3 Cab Rear - near rear door (Green)
Ch4 Cab Front - passenger seat shoulder height (Brown)
Ch4 Heater O/P Screen - Passenger side (Violet)

Notes- Windscreen Heater O/P thermocouple fell out as annotation but was returned. At about that time the engine had reached normal temperature
At 2nd Annotation heater control turned from full Hot to full Cold

As you can see the heater belts out very hot air (+80 C) but when turned to off it drops to a low level (not consistent with edo comment above). My defender does not have A/C fitted.

I may repeat test with other settings such as intermediate settings of the temp control knob. "You are never to old to learn something new"

28th Dec 2018 5:04pm

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