Am interested to know, if you have a heat pump, does it need to run constantly or only when you have the heating on or are using hot water? If it doesn't run constantly then is there a risk in winter of the water in the pipes freezing?
On air source systems, where the likelihood of exposed pipes above ground is higher, they should contain antifreeze which should be protected to the recommended manufacturers levels. On ground source systems, the ground collectors are also required to be protected generally to some lesser degree.
When you have a hot water storage tank - the heat pump will continuously keep the water to a certain temperature (anywhere between 45oC - 55oC) depending on the heat pump. Some high temperatures will keep it hot up to 80 oC. When the temperature drops to a certain level, the heat pump engages and tops the water temperature.
When you have your heating on in the winter - the controller works a little like a boiler. The heat pump will prioritise your hot water production, when the hot water has reached it's temperature, it then switches to provide heating through your wet distribution system. When the heating has reached it's set point through the thermostat - this switches the heat pump off until the temperature drops on the heating system. At this point - the heat pump switches on again to top up the radiators / underfloor heating system.
A well designed heat pump will run for fair periods at a time - an oversized heat pump will cycle on and off many times - where as an undersized heat pump will run constantly whilst struggling to reach it's set points.
Heat pump systems can provide homeowners with a simple, reliable, quiet and low-polluting means of home heating and cooling.It’s difficult to find a widely representative average cost for a GHP system, but recent studies found the average total installed cost including drilling — for a 10 kW, 3-ton thermal capacity system for a detached rural residence in the USA at $14,000 in 2008 dollars.The initial cost of installing a geothermal system can be several times that of an air-source system of the same heating and cooling capacity, but it’s offset as GHP systems have the lowest operating costs of any HVAC option. Annual energy savings of 30%-60% are typical and depend on factors including the availability of financing and incentives, which can result in substantial cost savings.
Last edited by HEA on Mon Oct 10, 2011 8:59 am, edited 1 time in total.
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I was just wondering if this is something that's dependent on the type of thermostat in use, but have any of you experienced that during cold weather (below 25F or so) your heat pump runs non-stop, maintains set point temperature, BUT does not actually get past it. Here is what I mean. What is noticed is that during cold days/nights my heat pump has no problem maintaining stat's set point, but instead of reaching it AND going over it, it reaches it, keeps it up, but never goes over it - runs all time.
With heatpumps it is critical that the system is designed well and installed correctly, near enough is not good enough. Why? If the heatpump is undersized, or the installation is poor, your system will constantly be "calling" Your heatpump for more, if it can not cope it will run continually. A heatpump is normally callculated to be 85% of the total demand required, so when it is very cold it may well run continually, however for the rest of the year it will run in long cycles, which is what makes them so efficient, if the heatpump is over sized, for most of year it would run in short cycles, IE stop start, making it inefficient. Try turning you thermostat down just a little and see if that helps, of turn down some thermostatic rad valves in rooms that you do not use, or if you have a secondary heatsource like a woodburning stove, stoke that up to try and get some heat into the house. Also, how well is your house insulated? If you are not letting the heat escape from your house, then you will not need to keep putting it in. Hope this helps Earthstore Energy
I am in the process of a self build and having an air source heat pump installed, from my research and questioning an ideal heat pump should rarely turn itself off, as a heat pump that constantly turns itself on and off through the day will use more energy than is requried and thus electric bills and usage will be increased.
I have been using a company called http://www.thermasys.co.uk , who have been really helpful in answering any questions that I have. Initially I was cautionary in my approach to heat pumps, but I am happy with my choice, I just hope I am happy when we are finally in our new home!
However, I recently visited a new build timber frame home that had an air source heat pump, it was approx 300m2 and its electric bill for everything inc oven, lighting etc was only £1300 a year, that is through the coldest winter in 30 years.
£1300/year for a 300 m2 property equals a SAP rating of 75 which is OK, but not great, for a brand-new property - though it is a very good rating for an electrically-heated property.
Even a detached house nowadays one would expect to get a rating better than 80 which would put the costs below £1000/year. Though anyone who can afford to build a 300m2 property probably isn't fussed about a £300/year difference!
I'm not sure that last winter was all that cold - yes, there were certainly some horrendously cold spells but I believe the average over the winter wasn't unusual.
Edit: on second thoughts, £300 is probably what the non-SAP energy consumption (appliances, cooking) costs, so £1000/year for SAP energy and a rating a little above 80 - excellent for an on-peak electricity heated property, but run of the mill for mains gas.
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