Saturday, September 24, 2011

Thermoelectric dehumidifier

Thermoelectric devices are solid state heat pumps. Their main drawback is that they have a very poor efficiency, they use a lot of electricity that is wasted as heat. The key is to find applications that will use the waste heat. One application is a dehumidifier for cloth drying. Instead of dumping warm moist air outside in the winter, a thermoelectric humidifier can remove the water from the air and keep the warm air inside. A thermoelectric dehumidifier can also warm and dehumidify a bedroom, or a bathroom.
I started looking at how much it would cost to build such a dehumidifier. The cheapest thermoelectric element I could find is this one:
92Watts max, about 60 Watts optimal under 12V.
The following heatsinks may be attached to each side:
The hot side can be equipped with a 80mm fan, such as this quiet fan:
Noctua NF-R8.
The cold side heatsink should be set downward, with a drip pan underneath to collect condensates. Some form of temperature control should maintain the cold side just at dew point for maximum efficiency. A hygrometer should turn on/off the dehumidifier when needed. I have a 12V 100Watts power supply that would be ideal for this.
Estimated cost: $70.
A more ambitious system would use 10 thermoelectric elements in series, powered by 120VAC through a rectifier. This would use 700 - 800 watts of electricity, and provide about 1KW of heat, considering the effect of dehumidification.

The small 100W dehumidifier could be set in areas of high moisture, while the 1KW dehumidifier could be integrated inside the furnace.

Wednesday, September 21, 2011

Producing heat, comfort and food

I have been reading from other people's experiences, particularly, and got some good ideas I may try this coming winter.
First idea is to use dehumidifiers to increase comfort and produce some heat in the process. We could use two dehumidifiers in our home, one upstairs and one downstairs, each in the main living rooms. Our house is fairly damp, particularly downstairs, so a dehumidifier will increase comfort.
Second idea is to use a dehumidifier to dry cloth indoors. That should be fairly easy downstairs, by setting a small dehumidifier in the laundry room, with a drying rack. The dehumidifier could be set on a timer. For the upstairs laundry room, I will have to be a little more inventive.
Third idea is to grow plants indoors, using grow lights to compensate for short days. These grow lights will produce heat, that will heat the room. Basically, all the heat produced by the grow lights will be displaced from the main furnace. In theory, the grow lights won't use any extra energy. In practice, if I put the grow lights in the room where the furnace thermostat is, then the rest of the house will be a little cooler, or I will have to set the thermostat a little higher. Either way, it looks like growing plants indoor in the winter, using grow lights, does not use as much electricity as it appears at first. Plus I will have fresh salads all winter long.

Looks like I will have some fun projects this winter.

Wednesday, September 14, 2011

Good Solar Irradiance Reference

The following website is a good reference for calculating the amount of energy that will fall on a solar collector, depending on your location, the collector inclination, time of the year...

Solar Irradiance

I estimated my solar fraction using this calculator.
First of all, solar irradiance vs tilt:

I plan on installing two systems, one for hot water, and another one for space heat. The solar hot water system will be set against the garage, on a vertical wall, with some summer shading from the roof overhang. I used the following website to estimate how much shading the overhang will generate:
Sustainable Design.
Here is an estimation of the area of the collector that will get shaded, for each month:
Using these values, I can now estimate the solar fraction for a 100sqft collector (second row=consumption, 3rd row=solar fraction, 4rth row=savings):
I also calculated the excess heat provided by the collector, that could be used for space heating. The yearly value of this excess heat is estimated at $32.
Next, solar fraction for space heat, assuming a 300sqft collector (second row=consumption, 3rd row=solar fraction, 4rth row=savings):
The total yearly savings with a 100sqft hot water collector, and a 300sqft space heat collector, will be $776, out of a $1600 bill. Because we get bi-monthly electric bills, here is the savings for each billing period:
It is interesting to see that the Sep-Oct bill is lower than the Jul-Aug bill. Two factors explain that: the tilt, optimized for winter, and the overhang shadow. These are good features that will reduce summer overheating of the collectors.

Finally, i will add the estimated savings from a $8000 heat pump. The savings calculation assumed 73°F winter temperature settings (we are at 68°F), resulting in a $2000 heating bill (our total electric bill is less than $2000, with about 40% for heat, and 15% for hot water). Due to these false assumptions, the savings are inflated, so I applied a correction factor equal to the actual vs estimated heating bill:
Estimated savings from heat pump = $880 / year (assuming $2000 yearly heating bill).
Savings after correction = $352 (assuming 40% of $2000 total electric bill).

The solar system will cost less than $8000 (cost estimated between $4000 and $5000), yet provide twice the savings of the heat pump.
The solar fraction is estimated at 80% of heating bill, and 45% of total electric bill.

Monday, September 12, 2011

Hydronic coils

I have searched for hydronic coils to use solar heated water in our furnace. This coil appears to be the best for the cost:
Brazetek 24x24
At 230kBTU/h, it should provide some heat, even when the solar heated water is down to 110F. The static pressure on the blower may be a problem. I could also add a second coil, one upstream and one downstream of the blower, balancing the pressure while improving the heat exchange capacity.
Here is a page giving derating from lower water temperatures:
Water temperature derating
Assuming one coils as above (230,000BTU/h at 180F), the output at 140F will be 131,000BTU/h. At 110F, we can estimate the derating to be 0.28. The heat output will then be 64400BTU/h, or more that 5 tons of heating, which should be enough.
The coil will be installed below the blower, where there should be enough room. The assembly that will hold it, will also hold a paper filter upstream, to prevent accumulation of dust in the coil. The coil+filter will replace the old dirty filter that is there now.

I also found, from, a source of solar tanks of big capacity:
American Solartechnics.
The best fitting tank for the furnace room is the 420 Gallons tank, measuring 43" x 76" x 54". That room could handle a 48" x 96" x 48", but that size doesn't exist standard. 420 gallons should provide enough storage capacity for most of the year. The tanks can handle 200F.
For the hot water system, their 110 gallon tank, at 34" x 34" x 54" will fit nicely. It could be coupled with a tankless electric water heater. The tank plus heat exchanger cost less than $2000. I'll have to compare that to other manufacturers. There is also the possibility of building it myself, which should be doable for the hot water tank, but difficult for the space heating tank, due to its bigger size.

Wednesday, September 7, 2011

Original Electric Furnace

In my quest to a more energy efficient home, I realized that re-using what already existed, and has worked for 20+ years, might be a good idea. Also, this is good for carbon reduction ("Reuse"). So that means I need to assess what I already have, as far as HVAC. Our home is equipped with an electric furnace from Lennox, model E11Q5-941-1P with Honeywell control. Here is a picture of the whole furnace:
Here is a close up on the label:
And here, the electrical wiring schematic:
From the information I have gleaned so far, this is a switched system, meaning it doesn't have a sequencer like modern electric furnaces. Instead, relays are used. Maybe this is a good upgrade to make, installing a sequencer. The blower is a 5 speed blower, although only two seem to be used (unlike what the wiring schematic says): Low speed for startup, then high speed.

Here are the features I can so far understand from the wiring diagram:
5 heat strips, or "element-electric heat", element 1&2 on circuit breaker 1 (CB1), element 3&4 on circuit breaker 2 (CB2), and element 5 + blower motor on circuit breaker 3 (CB3).
Each element has its own limit switch, although they are all called S2 on the wiring diagram.
Switch K1 drives the blower motor. This is the switch that is turned on when the thermostat manual switch is set to run the fan. If K1 is OFF, and K2 or K3 is on, then the blower runs at low speed. If K1 is ON, then the blower runs at high speed.

I will have to research a bit more to understand how the thermostat drives the different switches. It looks like upon a call for heat, the thermostat will close K2, which will run the blower on low speed, and energize HE1, 2 & 5. K2 AUX contact will close, possibly after a delay (?), and energize K3, which will turn HE3 and HE4 on.
I don't fully understand how K2-AUX work, or how K1 is energized (aside from the manual switch).

Before I think of adding solar heat to the system, I must understand how this furnace works, and how I can upgrade it to run an auxiliary source of heat.