I am a building services project manager working on the early design stages of a building that was to use ground source heat pumps. The main contractor has discovered that they are over budget and have asked for value engineering solutions to lower the costs. We have been asked to carry out a comparison and redesign using air source heat pumps. We have since found that due to the de-frosting stage of the units and the fact that they use electrical compressors that we can not get the COP (efficiency rating) down to a level that triggers a grant payment to the end user. We have now switched our attention to gas absorption heat pumps as these have been used on other projects and their efficiency is comparable to GSHP. I have no real experience with gas absorption pumps and have been trawling the internet for explanations, schematics and case studies. I can see that the system uses a water/ammonia mixture as the transfer fluid and that there appear to be very few moving parts. I can see that heat is applied to the mixture (presumably under the natural pressure created by the expansion of heating?)and the ammonia boils and separates from the water. The ammonia then condenses against a heat transfer surface giving up its heat to a secondary heat transfer i.e. water or air for distribution to the building. The condensed ammonia then falls to a collector and is mixed with the water again in an absorption chamber and the process starts again.
Questions
1. How much heat is required to be applied to the water/ammonia mixture? Ammonia boils at -33 deg c.
1a. Does the ammonia vaporise or stay as a liquid when heated under pressure?
1b. Presumably the ammonia, if a liquid under pressure and heat, will de-pressurise and transform into a gas - this cycle then would resemble the standard refrigeration air conditioning cycle.
2. What temperature is the ammonia at the point that it transfers its heat to the water/air for distribution?
3. What creates the movement of the water/ammonia mixture in the system? I don't know if there is generally a pump or if its the movement caused by temperature change and therefore pressure.
Perhaps i have this all wrong only to be put right. I have made an appointment to meet with some manufacturers but wanted to get as much information as possible before hand.
Questions
1. How much heat is required to be applied to the water/ammonia mixture? Ammonia boils at -33 deg c.
1a. Does the ammonia vaporise or stay as a liquid when heated under pressure?
1b. Presumably the ammonia, if a liquid under pressure and heat, will de-pressurise and transform into a gas - this cycle then would resemble the standard refrigeration air conditioning cycle.
2. What temperature is the ammonia at the point that it transfers its heat to the water/air for distribution?
3. What creates the movement of the water/ammonia mixture in the system? I don't know if there is generally a pump or if its the movement caused by temperature change and therefore pressure.
Perhaps i have this all wrong only to be put right. I have made an appointment to meet with some manufacturers but wanted to get as much information as possible before hand.
