Amory Lovins of the Rocky Mountain Institute has long advocated the concept of "negawatts". For some reason many people have difficulty equating reduced energy consumption as having the same value to a utility as generating new energy... especially the people running the utilities. Think about it. If you reduce electricity in your home by religiously turning off lights that don't need to be on and reduce your energy consumption by 1,000 kWh this month, those 1,000 kWh can be sold to another consumer. Is that any different to the utility than building a generator to produce 100 kWh to sell to that other consumer? Actually, it is....
Energy modeling is usually considered time consuming and it's tedious. One of the primary reasons it's done at all in many architectural and mechanical engineering offices is simply to comply with LEED, the building code or various incentives. All too often the person tasked with developing the energy model is the least junior technician or engineer in training in the office...the person with the least experience about buildings and systems, and how they can impact the energy loads. Energy modeling, when used as the design tool...
Sewage heat recovery doesn't sound very exciting! But it's something most people simply flush down the drain without giving it a thought. After all, it's just waste, right? Well, actually not...it's a pretty valuable energy source / heat sink. Sewage from a building is generally flushed away from toilets, showers, sinks, dishwashers and washing machines at a temperature of about 65° to 75°F (18° to 24°C). That's what is considered a pretty low-grade heat...in fact most people wouldn't think of...
A GHX is not an energy source...it's not like a gas or power line, or even delivered oil or propane. These fuels are delivered to the building and are essentially an infinite energy supply (as long as someone pays the bill). A GHX is very much a storage tank that can be discharged and recharged depending on what is going on in the building it's connected to. When the building is being cooled, the GHX is being recharged with energy...when the building needs heat, the GHX is being discharged. The storage capacity of the GHX is...
Determining the equipment capacity for a conventional HVAC system is relatively simple. You only need to calculate the peak heating and cooling loads of the building if the building is connected to the gas grid. Looking up the size of the gas pipe needed to deliver enough energy to the building is as simple as looking it up on a chart supplied by the gas company. Selecting a cooling tower or air cooled chiller can be done from a catalog or supplier's website. There's more work involved in designing the energy source / heat sink for a GCHP system.
You might have been told that if your building is already well insulated and energy efficient there's not much point in considering a GCHP system. There simply wouldn't be a payback because of the cost of installing a GCHP system and GHX is so high that I'd never get a return on my investment. I'd like to dispel that myth!
A lot of people are familiar with district heating systems. Hot water or steam from a central heating plant is pumped through a network of insulated pipes to nearby buildings. Some district heating systems take advantage of heat produced by a combined heat and power (CHP) plant that greatly improves the overall operating efficiency. One of the downsides of conventional hot water or steam distribution systems is that the piping systems are expensive to install becaus they must be well insulated to reduce heat loss to the ground. Hot water / steam systems are not able to take advantage low grade waste heat sources such as
I asked a question at the IGSHPA Conference a couple of years ago in a room full of people who make their living in the GCHP industry...engineers, mechanical contractors, GHX contractors, etc. The question was "What percentage of the commercial projects you work on are institutional (schools, prisons, government offices, hospitals, etc.) versus work for private developers?" The overwhelming reply was about...
Several times we've been asked to design a GCHP system when the client has already drilled a test borehole (in a couple of cases 2 test boreholes) and had someone conduct a thermal conductivity (TC) test. The test borehole and TC test were conducted before the size and footprint of the building had even been established and there was no idea of what the heating and cooling requirements of the proposed building would be. What a waste of money! Don't get me wrong...
...Only that it does! One of the factors that drives the cost of a GHX is what kind of equipment and methods the engineer specifies contractors in the area are prepared to work with. Design software considers the placement of the pipe in relation to the earth's surface, other pipes, thermal properties of the soil, etc. It does not consider how the pipe was placed there. Simply put, it doesn't matter how the pipe was placed where it is...it only matters that it gets into the ground where it is needed in the most cost-effective manner possible.
In my blog I'll be expressing my opinions about what I've the learned about ground coupled heat pump (GCHP) systems over the last 30 years. I've been very fortunate to work with many interesting people who are passionate about this technology...engineers, geologists, mechanical contractors, drillers, excavation contractors...in different parts of the world. I've learned a lot from them and will be using this forum to pass on some of the things I've learned and feel are important. Please feel free to use this information if you feel it's worthwhile...hopefully you can avoid some of the same mistakes I've learned from.
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