Controlling a portable electric heater with a Nest Thermostat

Nest E thermostat with heater and control box

My love affair with the Nest E thermostat continues (see previous post).  I acquired a second one for about $80 for use in my bedroom that is heated exclusively by a portable electric heater. I'm using a 1500W Pelonis Safe T Furnace with a ceramic heater core that works very well.  Apparently these heaters are classics now - I have had mine since the 1980's! 

Pelonis heater and my relay control box

The relay box contains a 24VAC relay rated for 15 Amps and a 20 Amp circuit breaker.  I wired it with a 12 gauge power cord and a 3-prong grounded outlet for the output.

inside my thermostat relay control box

I put a neon indicator next to the outlet so I could be sure it was switching.

Here's the schematic:

This should work with any thermostat, but use at your own risk.  It is important to use 12 gauge wire in the box and power cord to carry the high load, and I felt better putting my own 15 Amp circuit breaker inside.
Among the things that I have learned to love about the Nest are that it automatically adjusts for daylight savings.  But also it can set back the temperature when I leave home by using the IFTTT app.  Plus it could not be easier to use, program and adjust.  And of course I have connected it to Alexa so I can adjust the temperature by voice command and from my phone from aywhere.

NEST thermostat for my Rinnai monitor heater

I heat my home in rural Maine with a combination of a DIY installed heat pump, propane and a large wood stove.  (Since installing the heat pump in March 2121 the propane is now used only as a backup).  I have 2 Rinnai monitor heaters - one in the living area and 1 in the guest bedroom.  The wood stove in the basement is capable of heating the whole house, but I only fire it up when the temperatures drop below 20F which is often in the winter.  This strikes a balance for me of cost and performance - and carbon footprint.  I cut and split about  20-30% of my firewood from my own property here in rural Maine

I have been exploring different ways of controlling the big propane heater in my living room.

It's a 20 year old model that has a manual switch that you push-on/push-off and a simple slider to set temperature.  

A while back I built an interface that allowed me to use a regular programmable wall thermostat to operate it by replacing the power switch with a relay, and that worked relatively well.  But my schedule is erratic and I wanted the option of remote control.  The NEST thermostat E is a very appealing thermostat, but I had considered it too expensive until I found a used one one on eBay for about $80.  (The newer E model lists for $169, and the previous one is $249 and these prices are way more than a regular programmable thermostat that sell for $45 to $65.)

Here's the hookup info for the relay I used to control my heater.

I used a 24VAC power adapter that I got on Amazon that is sold specifically for home thermostats. (As an Amazon Associate I earn from qualifying purchases.)

I also bought a 24VAC relay from Digi-Key (their part number: Z9722-ND ).  It was pretty simple to hook these items up with the 25ft. of wire that came with the adapter.  I did have to get inside the heater and install the relay in there, and it was not something I would recommend for anyone not experienced with wiring or electronics.

This setup works really well for me.  Here's what I like about the Nest in particular.  First, I can control the thermostat setting from anywhere using my phone.  The user interface is excellent and it is extremely easy to program a schedule.

I also like that I can review the history that shows hours of operation per day and the individual cycles.

And the main screen could not be simpler:

Since I have installed an Alexa echo dot, I can say: "Alexa, set the thermostat to 68" and she set's it instantly.  This is nice if I decide to get up earlier than the scheduled time because I can use the 2nd echo dot in my bedroom to turn the heat up before I go downstairs.  Or, similarly if I decide to knock off work early I can set it from my office using the app.

Another clever feature is that the Nest can be programmed to set the heat back if I leave home.  It uses the IFTTT app to geolocate my home and can tell when I leave the area.  Overall I could not be happier with the Nest and all its features.

In my next post I show how I built an external relay box to control a portable electric heater from the Nest E.

Energy efficiency and cost to operate of appliances

humidifier with data logger

In my last post I talked about a new humidifier I purchased after careful deliberation.  (As an Amazon Associate I earn from qualifying purchases.)  You see, when I add an electrical appliance to my home I give very serious thought to how much energy it uses and what that will cost.  By cost I mean actual dollars per month, but also the cost to the planet when considering carbon footprint of the emissions needed to power it.  For most of the year my solar power system covers all my electrical needs, but due to the lack of sun hours in the winter, I do use utility power.  I write this blog to raise awareness for those who do not yet have solar or other renewably sourced electricity.

When I got the humidifier, I took a basic set of energy readings and found that it uses 16 to 24 Watts depending on the setting.  I generally use the middle setting that uses about 22 Watts.  As such, this is an extremely efficient humidifier.  Since I only use it for 8 hours each night in my bedroom I assumed the cost would be quite low.  A quick calculation showed that it would use 5.2kW/month if used every night (which I don't).  I pay about 16 cents/kW here in Maine - so my monthly cost would be about 84 cents.  Not bad!  And here in New England our utility power is sourced partially from renewables (it's around 40-50% currently) so the carbon footprint is modest.

Data logger showing Watts of humidifier

But wait! There's more!  This particular humidifier has a humidistat (showing 20% in the image above), so it probably cycles on and off as needed to maintain the 40% humidity I prefer at night.  So I connected my data logger to the power cord (see image at top of the page) and logged readings every second for one night.  Here's what I saw:

At first glance it seemed like it was jumping from 20 to 22 Watts all night.  But let's zoom in on that data:

Aha! Now we see that it is cycling on and off with a duty cycle of roughly 45-50% and dropping down to a baseline of about 5W to power the electronics.  (That's actually about 2W - my logger calibration is a bit off).  So the actual cost is around half what I had calculated.  Neat!

Lets look at the cost calculations.  To get the monthly cost I started with the actual Watts and multiplied it by hours/day to get daily Watts used:
W per Day = W X Hours per day  (22 X 8 = 176)
Then multiplied that by 30 to get Watts per month
W per month = W per Day X 30  (176 X 30 = 5280)
This can be expressed as 5.28 kWh (we pay the utility company by the kWh)
Here in Maine I pay 16 cents/kWh, so I just multiply
$/month = kWh X $/kWh (5.28 X .16 = 84.48 cents/month)

But thanks to my data logger, I see that in reality I'm using about half that or less than 43 cents if I use it every night.  So even in the winter when I use utility power, the carbon footprint of this humidifier is relatively token especially when compared with all the other types (evaporative and steam) that use MUCH more power.

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Data logging refrigerator power

Since I had got my data logger out, I decided to log some other appliances.  Generally the biggest energy using appliance in a home is the refrigerator and my 20+ year old one is relatively efficient.  Shown above is my data logger connected to an adapter cable that can measure AC current in Amps that is  converted to Watts in the logger.  And yes, that cool blue night light doubles as a Volt meter - I'm really that geeky!

As you may know, your fridge does not run all the time.  Typically the compressor will be on about 25-30% of the time, and that is illustrated by my log above. The on time is about 10 minutes, an it's off about 33 minutes.  Those big spikes represent the starting energy of the compressor - they only last about a second and the utility meter can't respond that quickly, so it does not factor in to my energy costs.

So here's the math on the cost to operate my fridge
300 Watts X 24 = 7200W/day (if always on)
7200W X .25 = 1800W/Day = 1.8kWh (actually on 25% of the time)
1.8kWh X 30 = 54kWh/month (30 days)
54kWh X 16 cents/kWh = $8.64 per month (your cost per kWh will be different).

So if you use a KillAwatt meter or any other energy monitor to try and calculate your energy cost for a given appliance, you should always leave it running for at least 24 hours to get the average power usage.  Just looking at a power meter in the moment can give you a false impression of actual power consumption.

At the low end of the power spectrum is this heated cat bed that I got recently for my 16+ year old cat Maxx.  She loves it and stays in it all the time.  It is rated at 4 Watts and the surface temperature is just a few degrees above ambient.  I measured 73F with my thermal camera while she was not in it:

When I connected it to an energy monitor, I saw actual readings of 3.5 to 3.7W. Here's the heating pad inside:

Since this in on 24/7, it uses about 2.66 kWh/month at a cost to me of about 42 cents.  It's a small price to pay to keep Maxx happy in her old age.  And she really likes it a lot!

Energy efficient humidifier

Click image to see this on Amazon

  

Recently my humidifier stopped working despite relatively frequent maintenance (OK I could have done better).  They all require frequent cleaning and rinsing out with vinegar.  I bought it in a hurry a year ago because I was having sinus infections due to the very dry winter air in Maine and this was relatively inexpensive and off-the-shelf at my local pharmacy.  But I liked being able to stick my face in the warm mist to soothe my sinuses and I could add scent to it which was pleasant.  In retrospect I should have done more research and made a smarter choice to get a more energy efficient unit.

So this time I took my time and studied up on humidifiers and how efficient they are.  I found a very helpful blog post: "How Much Energy Does My Humidifier Use?" that really clarified things.  It verified what I already knew intuitively as an engineer.  Basically there are 3 types of humidifier:

1. Warm mist units that boil water to create steam.  This is the type that I had and it used over 250 Watts.  Not very efficient!  Actually this type are the least energy efficient.  Vicks make several models that I often see in the local pharmacy.

2. Evaporative units blow air across a wet wicking material using a fan that consumes around 50 Watts.  I had one like this years ago and had issues with it.  First the fan was quite loud - even on low.  

And second I had to replace the wick material every few months as they built up mineral deposits and mold.  Also, I did not like the idea of creating waste.  The wicks cost around $7-10 each and were not available in-store when I needed them.

3. Ultrasonic humidifiers use an ultrasonic device that agitates water so it creates water vapor directly, then a small fan pushes it out into the room.  These units are very quiet and relatively affordable - starting at around $45, but you can spend a lot more.  They use a lot less energy.  At 20-30 Watts they are the most efficient type of humidifier.

So I settled on a model I like, this model has good Amazon reviews.

(As an Amazon Associate I earn from qualifying purchases.) 

I did some energy tests and found these readings:
Standby 2W
Low 16W
Medium 20W
High 24W

I also like the control features - they have geek appeal.  Not many humidifiers in this price range have a built-in humidistats and this one let's you set the humidity in 5% increments and displays it in 1% resolution.  It has 3 speeds, none of which make any noticeable sound, I just hear the occasional burble as air comes up into the tank like you would hear from a water cooler.  It has a timer so you can set it to run a certain number of hours.  I only use it at night, so I just turn it on as I go to bed, and set the humidity to 40 and run time for 8 hours.  It works perfectly and maintains an accurate humidity.  And to cap it all off there's a blue LED night light "feature" that I never use, but the geeky designers just had to throw that in!

I also looked specifically for a model that has a flat top for the water tank.  Very few of them do, and it is really helpful to be able to set it upside down in the sink for filling where it will be stable while filling it.  I mean seriously, how are you supposed to fill this one (shown at left)?

As a product designer, I am shocked by the poor ergonomics of most humidifier tanks that have useless "sexy" curves that simply fall over when you place the tank upside down in the sink - requiring you to hold it while filling a gallon or more.  Some of them have dark plastic water tanks that don't let you see the water level which is really dumb!  This is another reason I chose the model I'm using, I can clearly see the water level.

What is impressive about all ultrasonic units is that they start generating cool mist almost immediately.  No waiting for the water to boil and the mist is quite visible so you know it's working.

I'm filling my tank with filtered water and find that it uses 1/4 to 1/2 tank every night in my small bedroom.  So I can go 2-4 days before needing to re-fill the tank. 

 

Also note that it's important to maintain these units per the instructions.  This means soaking the bottom part in white vinegar every few weeks to prevent buildup of calcium deposits.  Read the instructions carefully! 

I'm looking forward to a reduced electric bill next month.  I only pay for electricity for about 4-5 months of the year due to my solar panels, and it really bugs me to have to pay the utility company.

See my next blog post for a detailed evaluation of the power consumption of my humidifier.   

Solar power backup - my dirty little secret

solar panels right before I cleared then in the morning

When I tell people that I have a solar powered home they tend to assume that I have battery backup for power outages.  I don't.  I have a grid intertied system, so any excess power I generate gets fed into the grid for which I get a credit under net metering rules.  In essence the grid is my storage, because I can use up that credit in the fall and winter.  When the power fails my solar power system shuts down to prevent my power from back feeding into the grid and harming line workers (this is a federally mandated safety system).   

By not having a battery I have to use a different strategy to survive the winter storm power outages that average 3 days each year here in rural Maine.  Some outages have run over 7 days, while other are just a few hours.  I need power to run my home based business, well pump, heating systems, refrigerator etc.

Since my solar power system is not designed to incorporate battery backup, I decided to install an automatic home backup generator that runs on propane.  This generator starts up in 15 seconds and powers my whole property - house and workshop. Yes, I'm burning fossil fuel to generate power!  But the cost performance trade-offs made sense at the time.  

My 5kW Generac generator only cost me about $2500 in 2009 from Home Depot and has 700 hours on it as of January 2019.  I installed it myself and do most of the basic maintenance, but also pay for maintenance and repairs as needed.  The cost of installing a large battery bank would have been more than double my modest investment.  Lead acid batteries need frequent maintenance and replacement every 5-7 years and the cost just did not make sense to me.  Batteries also have a very finite amount of energy storage lasting maybe a day or so without recharging whereas the stored propane in my tanks can provide power for almost 2 weeks if needed.

After every snow storm, the first thing I do is clear the solar panels and collectors - even if the power did not go out.  If the power did go out, the generator turns on with in 15 seconds.  I want to get as much free solar energy as possible.  So I have a long snow rake that I use to remove all the snow - usually in the morning before the sun hits the panels.

Click the image to see a time-lapse video of me clearing the snow on my property and solar panels in February 2018. 
There has been a change in the solar industry in the last year or so.  They are now offering home battery backups - whether or not you have solar power.  This is due the the plunging costs of large batteries like those use in electric vehicles.  Enphase, the company that makes the microinverters that I use have introduced just such a system, and there are many others like the Tesla Powerwall.  Click here for details about the Enphase battery system.  And click here to read an informative blog post from Energy Sage about Tesla Powerwall cost realities.  At some point I hope to install a system like this, but for now it is beyond my means.

First major boiler repair since I installed it in 2001

The solar augmented heating system I designed and built for my workshop back in 2001 has performed very well (details on my web site).  Maintenance has been minimal as far as the equipment itself is concerned the only part that failed was a pressure tank in 2010 which was easy to replace.  The boiler is only used to augment the stored solar heat in the 40 gallon storage tank so it rarely is running full blast.  It just needs to add enough heat to bring the temperature up to 140F for my radiators.  On a typical sunny day in winter the water in the storage tank is over 150F by the late afternoon.  As that gets drawn down to about 110F the boiler makes up the difference.

A week or so ago I noticed that the exhaust blower for the Bosch Aquastar boiler was not running and my utility room was hot and smelled like propane fumes.  The heat was due to the stalled motor that was getting really hot.  The bearings had seized so it could not remove the hot exhaust.

The Aquastar boiler itself has only required minimal maintenance over the last 18 years - good German engineering.  The blower motor has 22545 hours on it.  I know this because I put an hour meter on it to log running hours.  That's equivalent to 2.6 years of continuous operation!

I had to cut the blower off the motor shaft with a sawzall because the lock screw was frozen.  It took me an hour or so of web research to track down a replacement blower motor from one supplier and a motor from another source.  The parts cost less than $150. 

Removing it and replacing it required just a few bolts and screws, and wiring the new motor in.  The wiring in the control box was a total snake pit, but the motor only has 3 wires, so it was not too daunting for a skilled electrical engineer like me.

The new blower runs much quieter because the crud that had built up in the old one was making it run out of balance and it vibrated.
 
I enjoy repairing and maintaining the system that I designed and I hope that it will continue to work for many years.  Click here or on the image below to see live performance of the system.

If I could afford it I would replace the solar collectors and storage tank with an air source heat pump and keep the boiler and radiators as a backup.  Heat pumps are better bang for the buck these days.  Solar collectors for building heating are no longer cost competitive both from a performance standpoint and on and return on investment.

Rechargeable emergency LED lights

Recently I came across a new product that I have found to be helpful.  This is an LED lamp that looks like an ordinary 60W equivalent lamp (9W actual) that contains an internal battery.  The battery charges during normal usage - while the light is on.  Then if the utility power fails the internal circuitry detects this and powers the lamp for up to 3 hours (if it is switched on).  You can't test it by unplugging the light, it needs to be plugged in when the power fails.  I found a 2-pack for under $20 on-line.  (Click here to purchase on Amazon - As an Amazon Associate I earn from qualifying purchases.)

As I played around with them I learned a lot.  First, they come with a socket and hook with a button switch.  This allows them to be used for camping or location specific emergency lighting.  The way they detect an outage is to sense the resistance in the electrical wiring of the house, so the switch just shorts the contacts to turn the lamp on.

You can also turn the lamp on by touching the bottom of the lamp with a damp cloth - or your fingers.  (You can also do an "Uncle Fester" and put it in your mouth to light it by using your tongue to connect the contacts). 

When powered from 120V, they  produce 60W equivalent (850 Lumens) of bright warm light.  On internal battery power the output drops to 40W equivalent (500 Lumens) which is quite bright and useful in any situation.  The battery will last 3-4 hours and you can turn the lamp on and off after a power failure just like a normal light. If it is likely to be a long outage, you could conserve power buy using it sparingly.

I tried replacing lamps in my home with varied success.  First, I installed 1 in my kitchen ceiling where I have 4 flood lights, it came on when I turned the lights off.  I think this is because it sees the other 3 regular LED lights in the circuit and gets confused.  Also it is useless with any remote controlled home automation switch because the internal relay will switch it off when the power fails.  Same goes for room occupancy sensors that will turn off when the utility power fails and can't be turned on.  So these are most useful when used in table and floor lamps or house lighting circuits with only 1 lamp.  I'm also using them in my stairwells and hallways for safety.

If I still lived in California where earthquakes could knock out power I would use them widely as emergency lights.  Here in Maine, we get outages often in winter storms and they can last hours to days which is why I have an automatic standby generator that can power the whole property for over a week running on propane.  But the generator takes up to 15 seconds to start and these lamps will bridge that gap which I find compelling.  

Failing first generation microinverters

I installed my first array of 26 solar panels back in 2009 using state of the art microinverters made by Enphase.  I was an early adopter of the new technology that has created a paradigm change in solar power systems.  Previously an array of solar panels was wired in to a single large inverter that converts DC power from the solar panels to 240VAC that feeds in to the building.  

Microinverters are mounted behind each individual solar panel.  This creates a granular system that allows precise monitoring of the power produced at each panel.  It also offers a more graceful failure mode, if a single microinverter or panel fails, the whole system does not go down as it would with a large central inverter.

Over the years several of these first generation microinverters have failed and Enphase have been very responsive about sending out replacement units, honoring their 15 year warranty.  Of the original 26 inverters, 4 have now required replacement.  More details here.

It is tedious to have to go up on the roof using 2 ladders with a helpful neighbor and remove one of the panels and replace the inverter below it.   I hope the replacements will last longer!  As an electrical engineer, I recognize that the electronics are operating in the harshest conditions of heat and cold up on the roof and clearly there has been a learning curve as they gather data from failed units and incrementally improve the design.

Heating my bedroom - recovering chimney heat

In my last post I explored optimal ways to heat my bedroom using a small electric heater.  In this post I will detail how I have diverted trapped heat from around the chimney in the hallway to heat my room.  The chimney is cinder block and was exposed when my ex and I bought the house.  It was pretty ugly so I boxed it in with drywall on both floors, being careful to keep combustibles several inches from the hot surface.

The large wood stove in the basement is big enough to heat the whole house as heat rises from the open basement stairs and 2nd floor stairs to the bedrooms and bathroom.  The pictures below show the first floor boxed in chimney and the vents I installed to release the trapped heat.

   

By ventilating the closed space around the chimney I am releasing heat that could build up and prevent a chimney fire which is an added benefit.  But the primary goal was to recover this trapped heat.

My bedroom is adjacent to the chimney and I had used a similar scheme to ventilate the walled in chimney on the 2nd floor, but the vents both were in the hallway.  I decided to move the upper vent into my bedroom to divert the heat there.  This drawing shows the simple change I made:

Here's the bedroom wall before I cut the vent:

  

As you can see the area near the chimney is warmer than the other walls - through 2 layers of drywall!

After cutting the hole and closing off the vent in the hallway, I immediately felt warm air exiting the new vent in my bedroom.

 

With only a moderate fire going the heat coming from the vent is at least 10F hotter than the ambient room temperature. 

And after keeping the stove lit for a few days it's a lot warmer at the top vent (105F).

So I'm hoping this recovered heat will reduce the electricity needed to heat the bedroom.