Figure 18 – Batteries vs. Hardwired
When I jumped into a smart home project, I was taken in by the nber of battery-powered, wireless devices. I thought hardwiring all the devices was best avoided. But it is not just a matter of battery replacement although battery replacement is a big issue. And not every single device will experience the need for swapping the batteries, typically it is the regularly used devices that conse more power. But here is an example of a sensor that is not just a motion sensor, but also a vibration sensor, as well as a humidity sensor. It’s also measuring how much light is in the room, which could drive an automation to dim the light according to natural sunlight.
That’s a lot of sensing stuff going on. The vibration sensor is an anti-theft device so is it needed in all cases? It might be better for energy consumption if a motion sensor is just a motion sensor. A multisensor may not be the right tool for the job, even if it only costs a little more than a more simple sensor. All those additional things take up more energy and that means you’re swapping out batteries more frequently.
Although, if you hardwire these sorts of devices, they’re great. Many battery-powered smart devices come with usb ports for hardwired power. Only detached sensors like window
or door sensors really need to be battery powered. Or perhaps there is some flexibility here, as the USB port would allow for a very large external battery pack if a sensor to reduce the need for frequent battery swaps. The user will simply have a better experience with hard wired powered devices.
Figure 19 – Zwave and Zigbee
Another problem with some wireless smart home devices, such as lower than wifi frequencies like Zwave or Zigbee, is that the wireless devices are mesh rather than point-to-point. This means the devices rely on neighboring devices to relay their messages throughout the network, but the important thing to know about that, is the repeater stations need to be hardwired.
You can’t have a 100% wireless zwave or zigbee network, some of the sensors need to be hard wired otherwise they won’t be able to relay their messages back to the hub. So if you jump into a smart home with a bunch of battery-powered, wireless devices you’re going to have a bad time. You need to throw at least some hardwired devices into the mix.
Non-wifi wireless platforms like Zwave and Zigbee aren’t necessary if you trust your wifi security system, and can have worse performance than their higher energy wifi counterparts. But ultimately I choose Zwave or Zigbee devices when I need a generic product that can be integrated into a smart home system without dragging me into a cloud service provider. So at the very least, these non-wifi platforms make a good starting point for a smart home build.
Figure 20 – Wifi vs. Zwave vs Zigbee
Wi-fi operates at a 2400 megahertz or 2.4 gigahertz frequency, with new wifi going in at 5Ghz. Both Zwave and Zigbee are around 900 Megahertz. What does that really mean? Those old enough to remember hard-wired telephones as they transitioned to wireless corded handsets (before cell phones) might remember first generation product that didn’t have 20 or 30 feet of
range, replaced by a better phone later that had substantially more range allowing you to walk anywhere in the house. Z-wave and zigbee use that same frequency range.
So it’s not a new frequency and it’s not necessarily a better frequency than wifi. Wifi uses a higher frequency, which requires more energy for the same range. But wifi has a longer range than Z Wave overall, even if it means higher energy use. Maybe not all devices need that long of a range, but many do. Wifi can transmit more data, whereas Zwave tops out at around a 56k modem. Transmitting voice over Zwave would take up so much bandwidth it would not allow for any other Zwave devices to be on the network. Even though Zwave networks can hold about 200 devices at once, how chatty the devices are matters as do other considerations.
Real time energy metering requires a lot of data. In the energy controller section to come, I select a Zwave consumption monitor, but I am using a small Zwave network. A commercial facility might opt for a wifi monitor instead. Alternatively, another common solution would be to run multiple Zwave networks. Part of the thrill and frustration of smart home design is like computer programming, there are many solutions to the design.
I don’t think the technical argents of Zwave or Zigbee are enough to justify the technology over wifi. Having fine-tuned sensor settings is more important for energy consumption, and while these settings are adjustable in the open-source software I use, you still have to figure them out and then set them up for each device custom. Later we’ll talk about a security hub that even has a z-wave or zigbee antenna for external device compatibility, but the company’s own sensors are on the 2.4 gigahertz wifi frequency, so what does that tell you about their decision as to which is better?
Z-wave or zigbee make a good starting point, and there aren’t many wifi solutions that don’t draw you into a cloud service, so again, Z-wave and Zigbee make popular smart home starting points and then ultimately a large project begins to look for wifi solutions for a more stable, less limited communication solution.
Energy controls also make a good starting point, because smart technology can save the end user money. National Renewable Energy Labs states that the majority of the population will embrace energy efficiency products which yield a 1-2 year payback. Unlike solar, an energy controller will never eliminate 100% of an electric bill. But in a similar fashion to batteries, it can actively shift a portion of the electrical load from peak to off-peak use, for substantially less cost than batteries.
With an energy controller, the energy data is not simply monitored, but also acted upon by turning the right devices on and off. If everything necessary to do so is on a z-wave
Network, then energy controls can be implemented without requiring access to custom wifi.
This means the systems can be pre-programmed and tested offsite before installation, reducing the technical difficulty in the field. Certain customers may not allow smart devices to access their networks, yet nonetheless have a need for onsite energy controls.
Figure 21 – Wireless Frequency Comparisons
Z-wave or zigbee systems represent less of a threat to a corporate network, especially if they do not have wifi capability. Without the right antennae, it makes it impossible for one smart wireless device to hack the other. Likewise hackers are less interested in these systems as there is less valuable information – wifi devices make for bigger fish.
But although Z-wave or Zigbee can have encrypted communication, that requires more data bandwidth so a large encrypted z-wave or zigbee network is not feasible. Certain devices, such as door locks, require encryption. But encrypted pathways can only be relayed through encrypted relay stations. So for a door lock, is it more secure to be Zwave versus wifi? The answer might depend on user priorities, but I would lean towards higher end wifi. I would only recommend a Zwave door lock when the lock is located within the same room as the hub, so at the very least Zwave door locks may not be well suited for projects where more than one lock is required.
So even though Zwave may have encryption, that doesn’t necessarily mean you are going to use it. Wifi devices are simply more capable than Zwave at crunching the nbers through a data network. A better product may be one that accepts this fact and makes up for the increased energy use with a larger battery. Again, the main reasons I select Zwave or Zigbee devices is that I know the devices will be smart and not attach the system to yet another cloud service.