Reduce AC costs energy, carbon & money

AC (not to be confused with alternating-current), ie air-con or air-conditioning is a very simple idea.


A simple idea, but as important as the air that we breathe.


To be comfortable inside a building, depends on what you are doing and who you are, but some good generalisations are possible.


Four things are key: temperature, humidity, air-flow and quality.


The last of these can be put to one side for the purposes of energy management in a simple sentence - maintain the filters, and know what maximum and minimum flow rates for comfort are (some systems have quality sensors, but I'm not addressing that today as I covered air quality recently in the black art of air quality , and I think there are more opinions than ants at a picnic.


Air conditioning as a phrase is usually reserved for systems that influence both humidity and temperature, whereas simple air treatment often refers to temperature only.


So lets think about replacing air in a building.


If the air that leaves is in a worse state than the air that is coming in, ventilation even without any treatment is beneficial.


So for example if you are trying to cool the building and outside air at 25.5°C (77.9°F) and the air is leaving at 28.3°C (83°F) it is doing cooling for free - so you want as much of it as possible (until extract temperatures fall). So for economy, you should ventilate as a priority over active cooling.


On the other hand, if you are heating, and outside air is below extract temperature - you obviously want move as little air as possible (and recover any heat you can from what is leaving if you have heat wheels, run-around coils or cross-over plates).


The above statements are not strictly true - if you have the ability to detect enthalpy, it can be that cool wet air contains more energy than warmer wetter air.  However, if you are using enthalpy control, it is important to be aware of the need to maintain humidity sensors (which are vulnerable to deterioration).


Free cooling is where you vent an unoccupied building at night when electricity may be cheaper and the cooling effect is greater, to mitigate a need to actively cool later.  Given good weather forecasts (kWIQly can provide to anywhere on the planet), it can be worth actively cooling at night as cooling plant is more efficient - especially if you have cool storage - an ice store or similar. For monitoring performance good weather histories are essential - refer ventilation rates and degree-days.

Humidity control usually involves drying by cooling to below the dew point - the temperature given air conditions where moisture condenses on a cool surface (think glass of beer :), or humidifying using steam pack or similar.


Evaporative cooling is achieve by letting air evaporate from a pool - this increases relative humidity, so is both most effective and beneficial in dry climates.  When viable it is much less energy intense than steam production to humidify or conventional compressor based cooling.


To save money - now is the time to do air conditioning repair maintenance (when AC repairs are cheapest ! )

Building Energy Management Systems Snakeoil

Either you are sick of hearing them by now or you are very, very, new to this game.

If the latter - good luck and get used to it - if the former, then lets start to get over it ! 

What ?  I imagine you asking (rhetorically) so I answer - the following hopelessly hollow phrases..

• Let's put the 'e' back into bms.
• You can't manage what you can't measure.
• Every building is different.
• The cheapest kW is the one you never spend
• Smart-XYZ
• Self-Adaptive Learning Algorithm
• Auto-tuning
• Self-commissioning

You know why ? - because every building control system is inherently the same. And that is a huge problem for the people who make them and sell them.  

Commodities they are, and the only differentiators are prices (which are falling), likelihood of going out of business (as many manufacturers do at alarming frequency), and the deliberate incompatibilities that are put in as booby-traps to snare the less knowledgeable buyer (think Internet Explorer iPhones and pretty much every closed protocol device)

So whether they are referred to as unitary controllers, nodes, programmable logic controllers, embedded supervisors, SCADA, etc etc  it really doesn't matter - they are the same.

In essence they can take inputs in, process them according to some algorithm, put responses out and to be really esoteric they can communicate via "man-machine interfaces" aka screen/keyboard and via TCP/IP and a bunch of other protocols (unless you really buy a pooch).  Beyond this they may have bits of network topology, data storage, protocol converters (why needed), routers and etc.

What did I just describe - well a smartphone can do all of that for under 99$ , so can arduino open source hardware and it costs peanuts in comparison with the black boxes sold by the controls industry, so can any computer.  So the hardware is a sham.

What about analog sensors, (the phone has them and they cost virtually nothing), relays (oh yes every button on a keypad is a digital input).  

No, in reality there is nothing to distinguish them from a hardware perspective.  And remember just because a sensor can feed a 16-bit value along a comms network, if it is a thermometer it will tell you a very very precise temperature +/- a huge commissioning and field wiring error.

So if the hardware is the same, then the software must be different - nope.

Ladder Logic Diagram

Sure how you tell it what to do may be represented in a different "language" or via a different programming "paradigm", but what it does is it converts analog values into digital values and back again (ADC and DAC convertors), and in the middle bit it's all digital, so it does everything on the basis of sets of AND and OR gates (which many years ago was represented as "ladder logic" which was a visual analogy of a wiring circuit that related relays (digital states).

So where is the difference.  Well sales technique counts for a lot (especially to the non-technical buyer), and then there are big words and euphemisms.  So for example a BEMS is a euphemism for a BMS (a euphemy is simply the opposite of blasphemy - it literally means "speaking well")

Beyond sales technique there are the human skills of what to tell the computer (that's what it is) to do.  And here there IS an enormous difference.  You can either buy a set of pre-programmed modules off-the-shelf, or you can get someone to programme the "computer", that actually understand what boilers and air-handlers do.  No they aren'tt light switches, boilers pre and post-purge, and no a PID is not a suitable solution for controlling a non-proportional response.

My tip to the energy manager,  take the controls salesman into your plant room and ask him to explain what a sedimentation vessel achieves between primary and secondary circuits beyond the obvious  (hint : hydraulic de-coupling of pumped circuits) .  If he (or she) can't, then get someone who can - most local HVAC contractors can put someone in the frame to do the job.

And if your control system has to be configured by an "in-house expert" apply the same test and then say no - It is an artifical differentiator to suggest exclusivity and sucker byers with higher prices - that game went out of style a decade ago.  the big-boys just have'nt all figured it yet.

Correction - some have - they call you cash cows - go and be assertive or go and be milked dry - the choice is yours !

If you think this article might help anyone or make them smile wryly - please do share it - and if you disagree and want to argue - I make mistakes - that's what the comments are for !

Why not also see what http://kwiqly.com can do for you ? - we don't sell or recommend controls systems - because it's all the same to you!


PS - Are you aware that you can get free heating and cooling degree-day data for anywhere in the world from us ?