As we get closer to the installation I find myself talking to more and more people about ground source heat pumps and how they work. There is a lot of stuff out there on the web that describes it and it can get rather complicated. I'm reading all I can but I am not to the point where I can explain it succinctly. I found this very high level description from a source in Canada. I am still looking for a good one that will help me explain this all very clearly.
The other question I get is how popular are GSHP systems? According to the wikipedia article on GSHP systems, there were "As of 2004, over a million systems installed worldwide" and "Each year, about 80,000 units are installed in the USA".
Another important question is "how much does it cost?" Sadly, it seems like a lot. Last year, I was faced with estimates of $16,000 to replace my 20-year-old oil-fired systems with a modern boiler and circulating water coil (hydronics). This GSHP system costs more. On the surface it appears to be a lot more but three things help mitigate that cost. One is that 30% of the system cost gets rebated from the federal government at tax time. For the water heater (the Geospring ASHP) the limit of that is $1500, but there is no limit on the rebate for the GSHP system. That brings the total system cost much closer but still well north of the new oil system estimates. The second thing that helps is that we were able to get a $15,000 zero-percent 5-year loan after getting a home energy assessment from mass-save. (They even gave us some cool new CFL light bulbs which achieve their full brightness much more quickly than the bulbs that I purchased a couple of years ago.) Still it'll cost more to install the GSHP. The operating costs are expected to be much lower than my current system and also lower than a modern oil system + conventional A/C. We expect it to cost about $5000 more after full installation. And one must factor in the $15K interest free loan that I can pay out over the next 5 years.
The other issue with the oil-system upgrade (that we chose not to do) was that I'd have to consider getting my old chimney lined to accommodate the higher efficiency of the hypothetical new oil boiler. We had a quote for about $3000 to do that and it involved removing some bricks to get at a jog in the flue. That was not included in the $16000 estimate.
And for me, best of all is no more oil-system maintenance issues.
So what's next?
We expect the drilling to begin this week. After the drilling, they have to install the pipes in to the 2 6-inch holes and fill them with a thermal grout. Then they excavate a trench from the holes to the house and bore holes in the foundation about 4 feet underground so that the pipes can be connected to the heat pump in my basement.
When they get to excavating for the foundation bore holes, because of the location, my installer will have to remove my existing A/C system condensers pumping down the refrigerant and disposing of it responsibly. Then we'll be without A/C for a while until the new system is going. Hopefully it won't be too long given how hot it has been lately...
When the air conditioners are removed from service I will get my electrician to wire the new electrical circuits and the plumber to hook up my Geospring water heater and holding tank. Can't wait!
Today, I flagged the in-ground sprinkler heads with the hope that the drilling rig and excavator can avoid destroying the ones they must traverse to get to the work area. We also had a couple of tree branches trimmed so that the drilling rig can get in to the work area next to my house.
Saturday, July 31, 2010
Tuesday, July 20, 2010
Geospring's little quirk
The GE Geospring hybrid air-source heat pump has a little quirk according to the manufacturer. If the input water is above the set point for the water heater (say 120 degrees F), then the water heater experiences what they call "run-away" heating and presumably destroys itself. This is important for people to know especially if they are hooking the geospring to a desuperheater! I guess this could be an issue too if people are warming water with solar water heaters in conjunction with the geospring.
The desuperheater takes cold water from the supply line, heats it up when the GSHP is running, and dumps hot water back in to the drain plug of the water heater. On my GSHP, the desuperheater can be configured to output hot water at either 150 degrees or 125 degrees.
To avoid the bug in the geospring, we are going to put a mixing valve in the pipe coming from the desuperheater in the ground source heat pump. The mixing valve is pretty simple. It is 3-connection device with a configurable temperature setting. It mixes cold water in with the hot water if the hot water is above the temperature setting on the mixing valve.
The desuperheater takes cold water from the supply line, heats it up when the GSHP is running, and dumps hot water back in to the drain plug of the water heater. On my GSHP, the desuperheater can be configured to output hot water at either 150 degrees or 125 degrees.
To avoid the bug in the geospring, we are going to put a mixing valve in the pipe coming from the desuperheater in the ground source heat pump. The mixing valve is pretty simple. It is 3-connection device with a configurable temperature setting. It mixes cold water in with the hot water if the hot water is above the temperature setting on the mixing valve.
Friday, July 16, 2010
Upgrading the heating system for my home
It is time to upgrade my home's 20-year-old heating system. It seems like a bit of an adventure but after the maintenance problems we experienced last spring, we really felt that we had to do something to improve the situation.
Current situation
My house is not very large, about 2300 square feet, and is fairly well insulated. I had an infrared scan and a blower door test a couple of years ago and the number one recommendation was that I get my heating system upgraded. A few other simple suggestions resulted from those tests, adding insulation in my attic, sealing the attic hatch more tightly, adding insulation in a couple of places that were leaky.
My house has a forced hot air system. Actually, it has two complete oil-fired furnaces for heating the air. One for upstairs and one for downstairs. I also currently have a third oil-fired water heater. It is direct fired, has its own burner. So my chimney has three exhaust sources all joined together and entering the chimney.
I asked the HVAC contractor who was involved in the building of my house why he did it this way. He said that if they had used one unit the A/C would have been too big and cycled even more quickly than the system I have now which -- in my humble opinion -- cycles too quickly already.
My chimney is external to the house and the flue is big - big enough to handle the emissions from the 3 furnaces all going at the same time. Think about all that cold air in the chimney. Since my house is relatively tight, I don't use a lot of heat. So the chimney is often pretty cold. So I have bad draft on the chimney. A few years ago, we installed a draft inducer. That is a fan that kicks in whenever any of the 3 furnaces is combusting oil. I never liked the draft inducer. It was really noisy and sucked a lot of air out of the house to create the draft in the chimney. To get enough air for the furnaces and the draft inducer, my HVAC guys cut two holes in the side of my house to get combustion air. This results in the basement being even more humid in the summer than it otherwise would be. So I run a dehumidifer to dehumidify my little portion of planet Earth, I guess. This year, as part of my maintenance nightmare, my oil company replaced the draft inducer.
Each one of the furnaces for the hot air is probably big enough to heat the whole house on its own. 87K BTU each. In the heating season, they cycle too quickly so that means they are inefficient and wasting oil. In the cooling season, they also cycle too quickly. I have a 2.5 ton condenser for the 1st floor and a 2 ton condenser for the 2nd floor. Because they cycle too quickly, they don't get the moisture out of the house. In both seasons, because of the oversized heating and cooling, the air often feels stale in the house. The new system should remedy this as well.
Bathroom Ventilation
One more ventilation related thing: my bathroom showers each have fans that take the moist air out of the shower and in to my attic where it vents in to the soffit! That is never a good idea. When I first noticed this, I decided we had to stop using the bathroom fans. The air flow in the attic is supposed to go in the soffit vents, not out of it! The air flows up the sheathing and out the ridge vent. So that moist air was not leaving my house, it was staying inside the attic. We are fixing this problem too. As part of my heating system upgrade, we're installing an ERV - an energy recovery ventilator. No more opening the bathroom windows all winter long! More on that later.
The New System
The new system will be a Ground Source Heat Pump (GSHP) for heating my air and an Air Source Heat Pump (ASHP) for heating my hot water (more about the ASHP later). Sometimes people say "geothermal" but I think that term is more for places like Iceland. A GSHP relies on heat exchange with the ground, which in my case is expected to be 50 degrees Fahrenheit year round at a depth of greath than 10 feet. The system calls for 2 6-inch holes about 300 feet each, 20 feet apart. A loop of tubing will run from the GSHP in my basement down in to each of those holes and back up in to the house. In winter we extract heat from the ground by pumping 30 degree fluid through a closed loop and heating it to 50 degrees. In the summer we dump heat in to the ground from my house by taking the warm house air and circulating it through that same closed loop tube.
There is an interesting feature on the GSHP called a desuperheater which will help heat the hot water mostly in the summer, and only when the A/C is running. We are also installing an energy recovery ventilator (ERV) to provide fresh air in to the air duct returns while reclaiming the heat that is in the air coming out of the shower fans.
Electricity
We're basically going to be using more electricity but will have no more visits from the oil company. I'm going to measure our electricity use more closely. To do that, I purchased a "TED" http://www.theenergydetective.com/ . I got the 5002 model so that I can put one measuring device on my main electrical service panel and one on the subpanel for the HVAC+H2O system. The TED works with the Google Power Meter. It transmits data about my power use on the electrical wires and another device picks that data up an transmits it over my home's ethernet wiring.
In Massachusetts most of our electricity comes from burning coal. My electric utility has an option to purchase energy from a wind farm for a few extra cents per kWh. One can purchase 50% or 100% of your energy from wind. I know that is just net energy entering the grid and my electricity is probably coming from coal, but I believe paying these extra few cents encourages more investment in wind energy and that is a good thing. Obviously it would be nice if we had more government subsidies for wind and solar and other renewable energy resources.
I was a little concerned that the house might not have enough electrical current to support the new equipment. One electrician did a load calculation and thought it would be close and gave me very expensive options for upgrading my current 200Amp service. (Electrical load calculations are rather interesting; maybe a topic for another day). Another electrician that I've used several times before and who has a good reputation locally thought that there would be absolutely no problem. I guess we'll find out once the TED starts reporting its data.
The big question in all of this is the auxillary electrical resistive heating. That aux heat uses a lot of electrical current and as a result is very expensive. The GSHP includes this auxillary heating option for when the external temperature is outside of the GSHP design's operating range and as a result it cannot keep up the internal temperature of the house. The aux heat is like emergency backup heat. The GSHP controls/settings use the electrical resistive heat when it cannot reach the programmed temperature at the desired time. I haven't seen how the controls work yet. One person I spoke with disabled his aux heat entirely. Another person that I spoke with set the controls so that it only uses the aux heat in really extreme conditions. The whole system is designed to keep the house warmer than we normally keep the house (in case we ever want to sell it to people who don't enjoy wearing sweaters). Maybe it won't get used that much. We'll see ...
Air source heat pump
The ASHP for heating the water is probably the most mundane part of the system. I'm using the GE Geospring hybrid water heater. This water heater claims to have an energy factor (EF) of 2.3. The energy factor of 2.3 means that for every unit of electrical energy I use, I get 2.3 units of energy for heating the water. It works by taking heat energy out of the air (from my basement) and using that to heat the water in the tank. Depending on various modes, it can also use electrical resistive heat to heat the water if there are demand spikes and the ASHP cannot replenish the hot water fast enough. The ASHP will also dehumidify my basement as a side effect of its normal activity.
For the first concern: Electrical resistive heating is pretty expensive. Not sure what to say about the eletrical resistive heating. My hope is that it won't get used. I'm going to measure and hopefully it'll work out. The desuperheater will help a little. And if it is really bad, I might consider doing some solar water heating.
For the basement temperature issue, recall that I mentioned that I have two combustion air holes in the side of my house. Well those probably have a much bigger effect of the temperature of my basement than the ASHP will be. I might even be ahead now that I can close off those combustion air vents.
In future posts I hope to talk more about all these things. We have lots of things to do in the next few weeks. Some tree branches need to be cut to make room for the drilling rig. I have to get the old oil system removed and also remove the oil from my 2 oil tanks. The only access to my property for the drilling rig (a big truck) is by traversing part of my neighbor's front lawn. So I am indebted to my neighbor for their allowing this access and their willingness to tolerate the damage that the rig and excavator will inevitably incur. The driller has a plan to minimize the damage. Stay tuned...
Current situation
My house is not very large, about 2300 square feet, and is fairly well insulated. I had an infrared scan and a blower door test a couple of years ago and the number one recommendation was that I get my heating system upgraded. A few other simple suggestions resulted from those tests, adding insulation in my attic, sealing the attic hatch more tightly, adding insulation in a couple of places that were leaky.
My house has a forced hot air system. Actually, it has two complete oil-fired furnaces for heating the air. One for upstairs and one for downstairs. I also currently have a third oil-fired water heater. It is direct fired, has its own burner. So my chimney has three exhaust sources all joined together and entering the chimney.I asked the HVAC contractor who was involved in the building of my house why he did it this way. He said that if they had used one unit the A/C would have been too big and cycled even more quickly than the system I have now which -- in my humble opinion -- cycles too quickly already.
I explored upgrading my existing oil heating system to a more modern one that uses a single boiler and a set of water coils that could run to each of the 2 air handlers and to the water holding tank. The estimates I got for that were lower than the cost of my current system. But I am tired of the oil furnace maintenance routine. I've had several different oil companies over the years and it was always hard to get them to do all the required maintenance. Seems like they'd have some good guys who did great work and some guys who just wanted to get in and out as fast as they could. The latter usually resulted in clogged heat exchangers, clogged nozzles, etc.
My chimney is external to the house and the flue is big - big enough to handle the emissions from the 3 furnaces all going at the same time. Think about all that cold air in the chimney. Since my house is relatively tight, I don't use a lot of heat. So the chimney is often pretty cold. So I have bad draft on the chimney. A few years ago, we installed a draft inducer. That is a fan that kicks in whenever any of the 3 furnaces is combusting oil. I never liked the draft inducer. It was really noisy and sucked a lot of air out of the house to create the draft in the chimney. To get enough air for the furnaces and the draft inducer, my HVAC guys cut two holes in the side of my house to get combustion air. This results in the basement being even more humid in the summer than it otherwise would be. So I run a dehumidifer to dehumidify my little portion of planet Earth, I guess. This year, as part of my maintenance nightmare, my oil company replaced the draft inducer.
Each one of the furnaces for the hot air is probably big enough to heat the whole house on its own. 87K BTU each. In the heating season, they cycle too quickly so that means they are inefficient and wasting oil. In the cooling season, they also cycle too quickly. I have a 2.5 ton condenser for the 1st floor and a 2 ton condenser for the 2nd floor. Because they cycle too quickly, they don't get the moisture out of the house. In both seasons, because of the oversized heating and cooling, the air often feels stale in the house. The new system should remedy this as well.Bathroom Ventilation
One more ventilation related thing: my bathroom showers each have fans that take the moist air out of the shower and in to my attic where it vents in to the soffit! That is never a good idea. When I first noticed this, I decided we had to stop using the bathroom fans. The air flow in the attic is supposed to go in the soffit vents, not out of it! The air flows up the sheathing and out the ridge vent. So that moist air was not leaving my house, it was staying inside the attic. We are fixing this problem too. As part of my heating system upgrade, we're installing an ERV - an energy recovery ventilator. No more opening the bathroom windows all winter long! More on that later.
The New System
The new system will be a Ground Source Heat Pump (GSHP) for heating my air and an Air Source Heat Pump (ASHP) for heating my hot water (more about the ASHP later). Sometimes people say "geothermal" but I think that term is more for places like Iceland. A GSHP relies on heat exchange with the ground, which in my case is expected to be 50 degrees Fahrenheit year round at a depth of greath than 10 feet. The system calls for 2 6-inch holes about 300 feet each, 20 feet apart. A loop of tubing will run from the GSHP in my basement down in to each of those holes and back up in to the house. In winter we extract heat from the ground by pumping 30 degree fluid through a closed loop and heating it to 50 degrees. In the summer we dump heat in to the ground from my house by taking the warm house air and circulating it through that same closed loop tube.
There is an interesting feature on the GSHP called a desuperheater which will help heat the hot water mostly in the summer, and only when the A/C is running. We are also installing an energy recovery ventilator (ERV) to provide fresh air in to the air duct returns while reclaiming the heat that is in the air coming out of the shower fans.
We don't have the option of "natural" gas where I live. The gas lines don't reach near my house. Currently natural gas with a modern furnace seems like it would be hard to argue with cost-wise. But it is a fossil fuel... (I always giggle when I think about the term "natural" gas. What a clever marketing term! Who doesn't love nature? ... Sigh.)
Electricity
We're basically going to be using more electricity but will have no more visits from the oil company. I'm going to measure our electricity use more closely. To do that, I purchased a "TED" http://www.theenergydetective.com/ . I got the 5002 model so that I can put one measuring device on my main electrical service panel and one on the subpanel for the HVAC+H2O system. The TED works with the Google Power Meter. It transmits data about my power use on the electrical wires and another device picks that data up an transmits it over my home's ethernet wiring.
In Massachusetts most of our electricity comes from burning coal. My electric utility has an option to purchase energy from a wind farm for a few extra cents per kWh. One can purchase 50% or 100% of your energy from wind. I know that is just net energy entering the grid and my electricity is probably coming from coal, but I believe paying these extra few cents encourages more investment in wind energy and that is a good thing. Obviously it would be nice if we had more government subsidies for wind and solar and other renewable energy resources.
I was a little concerned that the house might not have enough electrical current to support the new equipment. One electrician did a load calculation and thought it would be close and gave me very expensive options for upgrading my current 200Amp service. (Electrical load calculations are rather interesting; maybe a topic for another day). Another electrician that I've used several times before and who has a good reputation locally thought that there would be absolutely no problem. I guess we'll find out once the TED starts reporting its data.
The big question in all of this is the auxillary electrical resistive heating. That aux heat uses a lot of electrical current and as a result is very expensive. The GSHP includes this auxillary heating option for when the external temperature is outside of the GSHP design's operating range and as a result it cannot keep up the internal temperature of the house. The aux heat is like emergency backup heat. The GSHP controls/settings use the electrical resistive heat when it cannot reach the programmed temperature at the desired time. I haven't seen how the controls work yet. One person I spoke with disabled his aux heat entirely. Another person that I spoke with set the controls so that it only uses the aux heat in really extreme conditions. The whole system is designed to keep the house warmer than we normally keep the house (in case we ever want to sell it to people who don't enjoy wearing sweaters). Maybe it won't get used that much. We'll see ...
Air source heat pump
The ASHP for heating the water is probably the most mundane part of the system. I'm using the GE Geospring hybrid water heater. This water heater claims to have an energy factor (EF) of 2.3. The energy factor of 2.3 means that for every unit of electrical energy I use, I get 2.3 units of energy for heating the water. It works by taking heat energy out of the air (from my basement) and using that to heat the water in the tank. Depending on various modes, it can also use electrical resistive heat to heat the water if there are demand spikes and the ASHP cannot replenish the hot water fast enough. The ASHP will also dehumidify my basement as a side effect of its normal activity.
I also looked at a cool non-integrated ASHP called the North Road Geyser. It has an EF of 2.0 which is slightly less than the Geospring, but the nice thing about it is that it is a separate unit from the water holding tank. If the tank fails, I can buy a new inexpensive electric water heater and use the same old Geyser heat pump. The Geyser hooks in via two "T" connections at the drain of any existing electric water heater tank. That poses a problem for me: My house already has a passive recirculation system that hooks in to the drain. And there is the new connection from the desuperheater from the GSHP. I thought that would be too many connections at the drain of the water heater. The Geyser still looks like a really cool device though.The biggest concerns with the ASHP are that (a) it might resort to electrical heating too often and (b) is that it will lower the temperature of my basement.
For the first concern: Electrical resistive heating is pretty expensive. Not sure what to say about the eletrical resistive heating. My hope is that it won't get used. I'm going to measure and hopefully it'll work out. The desuperheater will help a little. And if it is really bad, I might consider doing some solar water heating.
Aside: The solar water heating systems I've found for that are more money than I want to spend right now -- even though solar water heating seems to make a lot more sense than solar photovoltaic right now. Although I have my eyes on the Dow Powerhouse solar shingles. They look really cool. Out later this year supposedly!
For the basement temperature issue, recall that I mentioned that I have two combustion air holes in the side of my house. Well those probably have a much bigger effect of the temperature of my basement than the ASHP will be. I might even be ahead now that I can close off those combustion air vents.
In future posts I hope to talk more about all these things. We have lots of things to do in the next few weeks. Some tree branches need to be cut to make room for the drilling rig. I have to get the old oil system removed and also remove the oil from my 2 oil tanks. The only access to my property for the drilling rig (a big truck) is by traversing part of my neighbor's front lawn. So I am indebted to my neighbor for their allowing this access and their willingness to tolerate the damage that the rig and excavator will inevitably incur. The driller has a plan to minimize the damage. Stay tuned...
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