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Air Source heat Pump
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<blockquote data-quote="scotston" data-source="post: 6646968" data-attributes="member: 32666"><p>clearly two threads over lapping now. But the principles and mistakes of heat pump design still seem to be a mystery to most. The basic principle of thermodynamics where heat flows from a hot source to a colder is the main driver. This and the handy relationship between temperature and pressure. The energy that is being used is in the flow medium either air or brine (water and antifreeze underground). The flow rates of both are fixed by the fan and the pumps respectively. The total energy available to extract is therefore based on the temperatures of the mediums. For air this varies with ambient, with ground this varies but is buffered by the fact that the soil takes a long time to react, ie a season. By spring time the ground will be substantially cooler than in autumn but has a whole spring and summer to recharge. That's why it's called a solar array. If you specify too small an array relative to the size of the energy removed, clearly the ground will freeze. Don't. An underground aquifer or borehole is still a fluid that is massively insulated from ambient and therefore gives you a steadier output. But in the case of borehole simply a compromise between space and cost. Avoid if you can. The colder the source fluid for both air and ground the worse the efficiency. But the efficiency is much worse if you demand high flow temperatures from either unit. Head to <a href="http://johncantorheatpumps.blogspot.com/2014/03/getting-best-from-underfloor-heating.html" target="_blank">http://johncantorheatpumps.blogspot.com/2014/03/getting-best-from-underfloor-heating.html</a> to see how the curve is biased toward improved efficiency if you have a cold source fluid but low flow temperature. This is where insulation and radiated specification comes in. If you use radiators, they are relatively poor emitters of energy and work best with high flow temps unless you increase the radiator surface area. Big fat ones typically running at 50degC flow. Similarly the heat loss in a house is clearly worst in winter and if you have either small or too few radiators or too small an underfloor heating system then you need higher flow temps to make up the losses. Reduce the losses with insulation works. Have a densely fitted underfloor heating system all serve to lower the required flow temp and vastly improve overall system efficiency. Even in cold temperatures. My ground floor only, underfloor ASHP system runs around 30degC flow in winter with a typical CoP of 3. It uses a scroll compressor to reduce the power requirement of the unit as it approaches its load target. Typically running at 1.8kw providing 6kw of heating at 30DegC and 2.2kw providing 48degC DHW. Passive house, highly insulated. My air tightness was 0.5 air changes per hour - through good design rather than expensive materials. The air handling unit retains 93% of the heat and passes this on to the fresh and very cold incoming air. This keeps the house fresher than any normal house with a very low humidity. If you're too hot open a window, makes no odds to the system. I have a 6kw wood burner that lives in the 50% glazed living room. The heat from this travels (eventually) into the air handling unit and is distributed throughout the house. I tend to run the ambient air in the house through the day at 19degC using the underfloor and then put the fire on at night, this switches off the underfloor heating. 3 logs gets me 21degC, 5 logs and it's boxer short time. Here endith the lesson.</p></blockquote><p></p>
[QUOTE="scotston, post: 6646968, member: 32666"] clearly two threads over lapping now. But the principles and mistakes of heat pump design still seem to be a mystery to most. The basic principle of thermodynamics where heat flows from a hot source to a colder is the main driver. This and the handy relationship between temperature and pressure. The energy that is being used is in the flow medium either air or brine (water and antifreeze underground). The flow rates of both are fixed by the fan and the pumps respectively. The total energy available to extract is therefore based on the temperatures of the mediums. For air this varies with ambient, with ground this varies but is buffered by the fact that the soil takes a long time to react, ie a season. By spring time the ground will be substantially cooler than in autumn but has a whole spring and summer to recharge. That's why it's called a solar array. If you specify too small an array relative to the size of the energy removed, clearly the ground will freeze. Don't. An underground aquifer or borehole is still a fluid that is massively insulated from ambient and therefore gives you a steadier output. But in the case of borehole simply a compromise between space and cost. Avoid if you can. The colder the source fluid for both air and ground the worse the efficiency. But the efficiency is much worse if you demand high flow temperatures from either unit. Head to [URL]http://johncantorheatpumps.blogspot.com/2014/03/getting-best-from-underfloor-heating.html[/URL] to see how the curve is biased toward improved efficiency if you have a cold source fluid but low flow temperature. This is where insulation and radiated specification comes in. If you use radiators, they are relatively poor emitters of energy and work best with high flow temps unless you increase the radiator surface area. Big fat ones typically running at 50degC flow. Similarly the heat loss in a house is clearly worst in winter and if you have either small or too few radiators or too small an underfloor heating system then you need higher flow temps to make up the losses. Reduce the losses with insulation works. Have a densely fitted underfloor heating system all serve to lower the required flow temp and vastly improve overall system efficiency. Even in cold temperatures. My ground floor only, underfloor ASHP system runs around 30degC flow in winter with a typical CoP of 3. It uses a scroll compressor to reduce the power requirement of the unit as it approaches its load target. Typically running at 1.8kw providing 6kw of heating at 30DegC and 2.2kw providing 48degC DHW. Passive house, highly insulated. My air tightness was 0.5 air changes per hour - through good design rather than expensive materials. The air handling unit retains 93% of the heat and passes this on to the fresh and very cold incoming air. This keeps the house fresher than any normal house with a very low humidity. If you're too hot open a window, makes no odds to the system. I have a 6kw wood burner that lives in the 50% glazed living room. The heat from this travels (eventually) into the air handling unit and is distributed throughout the house. I tend to run the ambient air in the house through the day at 19degC using the underfloor and then put the fire on at night, this switches off the underfloor heating. 3 logs gets me 21degC, 5 logs and it's boxer short time. Here endith the lesson. [/QUOTE]
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