The heat loss survey we had suggested a 16kW heat pump, as we have data from our gas boiler for the last 12 months we have a fair idea of the power needed by gas boiler, about 9kW. Heat loss engineers at a heat pump company dismissed the real data. If we had followed the suggested 16kW heat pump recommendation we would have had a heat pump cycling and reducing its COP. Net result we are sticking with our gas boiler for now.
A common refrain unfortunately. A friend got quotes for 12 to 16kW heat pumps. He eventually did his own heat loss calc, found a cooperative installer and put in a 5 kW ashp just over a year ago. It's working well.
@@sygad1 as someone who fitted an MVHR to solve a multitude of issues last year - and I'm very happy with it - I would also be very interested. In theory an MVHR, even if only 50% efficient at recovering heat, will make a huge improvement to a heat pump because when it's coldest the air coming in is very dry, relatively. This is exactly when you want drier air in the house as it takes less energy to warm up Vs humid air. Also trickle vents are ineffective in calm conditions and terrible in windy conditions, so if anything the consistent air flow from an MVHR and a focus on improving air tightness allows the "worst case drafty house" air change in MCS numbers to be dialed back. And it's easy to only focus on the temperature, cost and efficiency without considering the health and quality of life in the property. I'm so pleased with our MVHR: got rid of the tumble dryer, house is fresh always, rooms aren't cold from windows being open, more alert due to more oxygen... Love it!
Interesting comments about air exchanges. When I did a heatpunk survey the defaults seemed so high. My 1988 house just isn't draughty. I guesstimated it was more likely 1 or lower. A proper test is the only way to really know though.
We installed a geothermal heatpump in 2004 when we built our house. Walls have 200 mm of rockwoll plus a 13 mm windshield board and wood panel fasad, floor have 200 mm of styrofoam and leckablock foundation which insulates much better compared to old concreate or stone foundations, and roof have some 400-500 mm of blow insulation woll (thick because it needs to cover the ventilation pipes). Single outside glass and duble glassed inside glass filled with argon. The house is 208 sqm and the coldest day or DUT as we call it is -26 C. The well is 178 meters deep and water comming in is around 5 to 7 degrees normally. When it gets really cold below -20 for a couple of weeks it drops to 3-4 degrees, so not faar from your coldest days of a few degrees minus. There is floor heating both down and up-stairs. Max outgoing temp is +35 C. This is standard set-up for a house built before 2010. Nowadays it is 250 mm in the walls and polyurathene sheets in the floor, rest is about the same. All houses built after 1990 have fan driven ventilation system with a heatexchanger. In 2004 it was the practice here as well to underdimension the heatpump to cover 70-80% of the heating at DUT. The heatpumps were on/off types. The heat loss calculation recommended a 7 kW pump. I bought a 9.5 KW unit. The argument for not having a too big pump was that it would do to many starts and stops during all other days when tepreatures were warmer than DUT. However, even back then the heatpumps regualtion system was so good that I could manipulate the heatpump to make reasonable amount of starts and stops. It lasted me 20 years, and it was not the compressor that broke but the built-in water boiler. I replaced the heatpump last year. The most common model around here is a 3-12 kW inverter pump. Having the experience from 20 years I choose to buy a 2-8 kW unit. It has never been even close to needing to produce 8 kW even though we had a couple of weeks with -25 to -30 last winter. Average outgoing temperature in the floor in January was 32.8 C. The benefit of the unit is that during spring and easter it mostly runs at this 2 kW. The big unit would have run on minimum of 3 kW. I have on average 2.8 starts per day and the compressor have been running 47 percent of the time, mostly at this 2-3 kW generated heat output. The dimensioning should ofcourse be done so that it covers the coldest day by some margin but with the inverter pumps the lowest possible of speed of the compressor is also important. It should be easier with the inverter pumps to dimension than with an on/off pump. The only downside with an inverter is that it is another part that can fail or will fail. I did not ask for any advice when installing the new heatpump I just picked the one I wanted and had it installed. I am happy with that decision and confident that my system will heat the house down to -35. At those temperatures I will anyhow throw some firewood in the fireplace as the electricity price will most likely be sky-high. If for some reason I would not be home there is the slim possibility the direct electric heating would kick in but then we ate talking of the risk of below -40 degrees for weeks when I would zip on a pina colada in the Bahamas. It has never been bellow -40 here so far and as said it will be the price of electricity that is the big concern not if the house is +16 which I easily can cover with firewood when getting home. The insulation is probally much better here in general but 16 KW is more for some commercial building or if you live in a glas mansion with a swimming pool over here. I have a separate garage which I heat with a 2.5 kW air to air heat pump. It works fine and still gives around 2 in COP between -20 to -25. I would spend money on insulation; floor, roof, and windows to start with if somone recommend a 16 kW unit to me. Insulation do not have any running costs. And yes all rooms have the same temperature around +21,5 C in the winter. We normally pay 2000-2500 Euro per year on all electricity including heating, hot water and household electricity. The well and underfloor heating was an investment 20 years ago but replacing the thermal heat pump and the air-to-air heat pump, which is quite recent cost me 13 000 Euros. By the way all towns with over10-15 thousand inhabitants have central heating over here, even smaller villages if there is a industrial complex nearby producing extra heat, no need foor expensive heating systems. This is available for appartments as well as semi detached and detached houses closer to the city centre. Ths is normally the cheapest heating. All applinces run on electricity. No gas avilable here expect for in a few locations. Thanks for interesting video.
I think one of the main reasons heat loss calculations overestimate the size of the heat pump required is that the calculation gives the gross heat loss, and the heat pump is sized to supply this amount of heat, but this does not take into account other sources of heat in the house! Heat is supplied to the house from all the electrical appliances (including lighting, fridges/freezers, washing machines and tumble dryers, audio visual systems, etc. etc..), cooking, hot water use, people, and the biggie, passive solar gain through windows. A house with large south facing windows, and/or, as I have, a large glass roof lantern over a kitchen dining extension, will gain a lot of heat. Think about doing a heat loss calculation for a greenhouse, you'll come up with a very big number for the heat loss through the single pane glass, but completely missed the solar gain that the greenhouse is specifically designed to provide! You need to add a heat GAIN calculation from all the non-heatpump sources of heat to get a net heat requirement for the heat pump to supply.
You cant count on solar gains from this type of heat loss calc, because they need to work on that occasional cold overcast week in late Jan when there is almost no solar irradiance. What's more common is vastly overestimating air leakage rates or just getting wall, roof or floor U values completely wrong.
I have 3 monitors in my home office and today where the initial temperature was 17 deg before I started work and it ended up being 24 deg. It’s under insulted and the radiator is under sized based on the heat loss calculation I have done. So the monitors do a good job of pumping out usable heat.
Exactly! My TV and PlayStation 5 together use 400W in HDR game content - that's 50% of my lounge heat loss at design ambient temperature - and that's without people in the room too.
A poor heat loss calculation might lead to a larger heat pump which may cost a relatively small amount more as Graham says (@19:30) but that isn't the end of it. It will also lead to more radiator upgrades, bigger pipes, maybe even UFH that wasn't necessary. So saying it only adds the price difference between a 12kW and a 14kW pump is disingenuous.
I provide heat loss surveys for heat pumps and always try to benchmark my room by room heat losses against gas smart meter data where possible (80% of homes), which I then adjust downwards for gas boiler inefficiency and upwards or downwards depending on whether the homeowner keeps rooms cold or hot compared with MCS room temperatures. The MCS air change defaults are far too high, averaging 1.5 ACH (air changes per hour) whereas the average home at average wind speeds is typically 0.5 ACH, so the MCS by default overstates air permeability by a factor of 3. The MCS also has default U values which are far too high for many elements e.g. 2.1 for triple glazing whereas modern good quality triple glazing Uw's are typically 0.8 to 1.0. I spend a lot of time during the survey verifying fabric, trying to observe cavity wall depth and insulation, asking home owners when the insulation was installed, building reg certificates, invoices for new replacement windows etc. Generally using this more careful methodology my room by room heat losses are within 10% of the smart meter data. The MCS also doesn't account for internal heat gains: metabolic, appliances, hot water, solar etc., which is typically 0.4 to 1.0 kW which the heat pump won't need to produce. Where I have been asked to do heat loss calculations to check other installers calculations I see them typically 50% to 200% too high, worst case has been 400%. Often the root cause as suggested by the homeowner on the video is completely missing cavity wall insulation. The typical side effect of this is the heat pump short-cycles inefficiently, and that the weather compensation curves are typically set inefficiently too high. Generally oversizing the heat pump slightly is ok, some short-cycling appears not to reduce performance too much but getting weather compensation curves too high does reduce performance, but can be fixed post installation. Government research suggests that the average UK heat pump is 280% efficient, compared with Heat Geek installations which have more careful design which typically achieve 400%.
I'm slightly alarmed watching this video (which was a great discussion by the way) because I'm spending a lot of time and money upgrading fabric, radiators and airtightness to get ready for a heat pump as i renovate the house. But will any of that be counted by the MCS process? I've done two heat loss calculations (MCS and heatpunk) and have established all the materials and therefore likely U value around my house. I've used these calculations to guide me on the best bang for the buck renovations to do. Real data (meter and smart home devices) validate the calculations. Have i wasted my time if an installer is just going to stick to "out the box" MCS numbers?
I hired a company to do a full heat transfer measurement of our house, for all the components(walls, windows, roof…). I was surprised to find out that the heat transfer for the walls (Porotherm 25cm + 10cm EPS) was measured at U=0,45, instead of the “standards” of 0,27. Multiply this by the total area of the walls (210m2) and then multiply with the Delta T……you get the picture
Is there a workaround within the MCS system of oversizing? The default desired temp feel so high (22 degrees). Is this really a requirement in the UK. If not can it be reduced at the design stage? Impacting the heat loss as a result.
It seems the cusp is where the home is close to 14kw heat loss.. oversizing means 2 units and twice the cost…might as well leave the gas boiler just in case and forego the grant, and go with 1 unit. You are no worse off! Our house is 260 sq metres (very well insulated to 2016 building regs) - annual LPG usage suggests we need c. 9 kw. Heat loss calc suggests 15kw - 20kw .
Wall insulation question - can you not take the temp of the internal wall and the same spot on the external and have a calculation of the potential loss of heat?
Unfortunately, that's very inaccurate. The external surface temperature will be very dependant on wind speed and thermal radiation. An added complication is that cavity wall installs have often been fine badly with large voids, so the insulation can vary a lot from location to location. At the more extreme end, a friend of mine had all the cavity wall insulation guarantee paperwork when he bought his house but then found he had absolutely no cavity wall insulation actually installed. Presumably the "installer" pocketed the grant funding.
Heatloss of 100 W per sqm. Here it is normally around 20 in buildings from this century and up to 40 in older cottages. How do you actually build your houses, out of sticks?
Surely the biggest danger of using your gas usage to size a heat pump is that people use gas central heating very differently to a heat pump. For example, not many people with gas central heating will run their heating seven days a week, twenty four hours a day and have all their radiator valves fully open...
Can I please ask how do you guys factor in hot water demand and the effect it may have on the heating.For example we have just had a heat loss for a new build come back at 3,4kw but the client wants a 250ltr. Cylinder. Vaillant say the max size of cylinder a 3.5kw heat pump can heat is 200ltr because it would take too long for the 3.5 to heat 250 ltr from 10 degrees to 50 degrees
Our house is set to 22°c living room 24°c and even then my wife will feel cold. Our heatpump so far has worked well but I’m yet to have a full winter with it, so time will tell.
What do you think of the 'heating degree days' (HDD) method of predicting heat loss. From memory you download the HDD figure for your location, divide that figure into your total energy input (gas + electricity + solar PV in my case) and it comes up with estimate of heat pump sizing. Reason for the question is that I downloaded an Excel model from the net, fed in my figures and was told that my 3 bed, 1990's detached house needed a pump size of 3.4 kW which seems way too low to me. As an example my gas boiler modulates down to 5 kW and the heating load is more than enough to keep it firing continuously during winter. PSW - Would be grateful if someone could point me at alternative spreadsheets to experiment with.
Guys, you said divide gas usage by 2000 while this guys says 2900: ruclips.net/video/hCeghKa3liM/видео.html (see 8 mins 7 secs for the final calculation and 6 mins 45 secs for the explanation). That's quite a difference and I was wondering why?
Fair question, and I don’t know why Michael is saying 2900, but I would take Graham’s number of 2,000 because he is one of the most experienced heating engineers out there.
@@RenewableHeatingHub Michael de Podesta is a well known and respected Physicist. It might be worth asking Graham to take a look at the video I linked as the calculation is explained in detail. Would be good to know why there is a difference?
@@darrenadams2640The number 2900 vs. 2000 is actually a variable 'heating degree days', which depends on location. It's discussed in detail later in that video, at around 17 minutes. HTH
Using energy data isn’t the right way to go because as has been stated. What the current owner does could well be different to a new owner, for example I have my heating in twenty four seven others might not.
It shouldn't be used alone, but as the only empirical data to validate the heat loss calculations, it really can't be ignored either. MCS ignores other heat sources from people, devices, solar gain, and cooking. It hugely overestimates ventilation losses. It relies on accurate fabric U value estimations. Real data is real data - any installer who can't try to reconcile theoretical values to the real ones isn't worth working with IMHO.
The heat loss survey we had suggested a 16kW heat pump, as we have data from our gas boiler for the last 12 months we have a fair idea of the power needed by gas boiler, about 9kW. Heat loss engineers at a heat pump company dismissed the real data. If we had followed the suggested 16kW heat pump recommendation we would have had a heat pump cycling and reducing its COP. Net result we are sticking with our gas boiler for now.
A common refrain unfortunately. A friend got quotes for 12 to 16kW heat pumps. He eventually did his own heat loss calc, found a cooperative installer and put in a 5 kW ashp just over a year ago. It's working well.
Would like to see an episode discussing door blower tests and how to go about getting one and MVHR and how it works together with a heat pump
@@sygad1 as someone who fitted an MVHR to solve a multitude of issues last year - and I'm very happy with it - I would also be very interested.
In theory an MVHR, even if only 50% efficient at recovering heat, will make a huge improvement to a heat pump because when it's coldest the air coming in is very dry, relatively. This is exactly when you want drier air in the house as it takes less energy to warm up Vs humid air.
Also trickle vents are ineffective in calm conditions and terrible in windy conditions, so if anything the consistent air flow from an MVHR and a focus on improving air tightness allows the "worst case drafty house" air change in MCS numbers to be dialed back.
And it's easy to only focus on the temperature, cost and efficiency without considering the health and quality of life in the property. I'm so pleased with our MVHR: got rid of the tumble dryer, house is fresh always, rooms aren't cold from windows being open, more alert due to more oxygen... Love it!
Interesting comments about air exchanges. When I did a heatpunk survey the defaults seemed so high. My 1988 house just isn't draughty. I guesstimated it was more likely 1 or lower. A proper test is the only way to really know though.
We installed a geothermal heatpump in 2004 when we built our house. Walls have 200 mm of rockwoll plus a 13 mm windshield board and wood panel fasad, floor have 200 mm of styrofoam and leckablock foundation which insulates much better compared to old concreate or stone foundations, and roof have some 400-500 mm of blow insulation woll (thick because it needs to cover the ventilation pipes). Single outside glass and duble glassed inside glass filled with argon. The house is 208 sqm and the coldest day or DUT as we call it is -26 C. The well is 178 meters deep and water comming in is around 5 to 7 degrees normally. When it gets really cold below -20 for a couple of weeks it drops to 3-4 degrees, so not faar from your coldest days of a few degrees minus. There is floor heating both down and up-stairs. Max outgoing temp is +35 C. This is standard set-up for a house built before 2010. Nowadays it is 250 mm in the walls and polyurathene sheets in the floor, rest is about the same. All houses built after 1990 have fan driven ventilation system with a heatexchanger.
In 2004 it was the practice here as well to underdimension the heatpump to cover 70-80% of the heating at DUT. The heatpumps were on/off types. The heat loss calculation recommended a 7 kW pump. I bought a 9.5 KW unit. The argument for not having a too big pump was that it would do to many starts and stops during all other days when tepreatures were warmer than DUT.
However, even back then the heatpumps regualtion system was so good that I could manipulate the heatpump to make reasonable amount of starts and stops. It lasted me 20 years, and it was not the compressor that broke but the built-in water boiler.
I replaced the heatpump last year. The most common model around here is a 3-12 kW inverter pump. Having the experience from 20 years I choose to buy a 2-8 kW unit. It has never been even close to needing to produce 8 kW even though we had a couple of weeks with -25 to -30 last winter. Average outgoing temperature in the floor in January was 32.8 C. The benefit of the unit is that during spring and easter it mostly runs at this 2 kW. The big unit would have run on minimum of 3 kW. I have on average 2.8 starts per day and the compressor have been running 47 percent of the time, mostly at this 2-3 kW generated heat output.
The dimensioning should ofcourse be done so that it covers the coldest day by some margin but with the inverter pumps the lowest possible of speed of the compressor is also important. It should be easier with the inverter pumps to dimension than with an on/off pump. The only downside with an inverter is that it is another part that can fail or will fail.
I did not ask for any advice when installing the new heatpump I just picked the one I wanted and had it installed. I am happy with that decision and confident that my system will heat the house down to -35. At those temperatures I will anyhow throw some firewood in the fireplace as the electricity price will most likely be sky-high. If for some reason I would not be home there is the slim possibility the direct electric heating would kick in but then we ate talking of the risk of below -40 degrees for weeks when I would zip on a pina colada in the Bahamas. It has never been bellow -40 here so far and as said it will be the price of electricity that is the big concern not if the house is +16 which I easily can cover with firewood when getting home.
The insulation is probally much better here in general but 16 KW is more for some commercial building or if you live in a glas mansion with a swimming pool over here.
I have a separate garage which I heat with a 2.5 kW air to air heat pump. It works fine and still gives around 2 in COP between -20 to -25.
I would spend money on insulation; floor, roof, and windows to start with if somone recommend a 16 kW unit to me. Insulation do not have any running costs.
And yes all rooms have the same temperature around +21,5 C in the winter. We normally pay 2000-2500 Euro per year on all electricity including heating, hot water and household electricity. The well and underfloor heating was an investment 20 years ago but replacing the thermal heat pump and the air-to-air heat pump, which is quite recent cost me 13 000 Euros.
By the way all towns with over10-15 thousand inhabitants have central heating over here, even smaller villages if there is a industrial complex nearby producing extra heat, no need foor expensive heating systems. This is available for appartments as well as semi detached and detached houses closer to the city centre. Ths is normally the cheapest heating. All applinces run on electricity. No gas avilable here expect for in a few locations.
Thanks for interesting video.
I think one of the main reasons heat loss calculations overestimate the size of the heat pump required is that the calculation gives the gross heat loss, and the heat pump is sized to supply this amount of heat, but this does not take into account other sources of heat in the house! Heat is supplied to the house from all the electrical appliances (including lighting, fridges/freezers, washing machines and tumble dryers, audio visual systems, etc. etc..), cooking, hot water use, people, and the biggie, passive solar gain through windows. A house with large south facing windows, and/or, as I have, a large glass roof lantern over a kitchen dining extension, will gain a lot of heat. Think about doing a heat loss calculation for a greenhouse, you'll come up with a very big number for the heat loss through the single pane glass, but completely missed the solar gain that the greenhouse is specifically designed to provide! You need to add a heat GAIN calculation from all the non-heatpump sources of heat to get a net heat requirement for the heat pump to supply.
You cant count on solar gains from this type of heat loss calc, because they need to work on that occasional cold overcast week in late Jan when there is almost no solar irradiance. What's more common is vastly overestimating air leakage rates or just getting wall, roof or floor U values completely wrong.
I have 3 monitors in my home office and today where the initial temperature was 17 deg before I started work and it ended up being 24 deg. It’s under insulted and the radiator is under sized based on the heat loss calculation I have done. So the monitors do a good job of pumping out usable heat.
Exactly! My TV and PlayStation 5 together use 400W in HDR game content - that's 50% of my lounge heat loss at design ambient temperature - and that's without people in the room too.
A poor heat loss calculation might lead to a larger heat pump which may cost a relatively small amount more as Graham says (@19:30) but that isn't the end of it. It will also lead to more radiator upgrades, bigger pipes, maybe even UFH that wasn't necessary. So saying it only adds the price difference between a 12kW and a 14kW pump is disingenuous.
I provide heat loss surveys for heat pumps and always try to benchmark my room by room heat losses against gas smart meter data where possible (80% of homes), which I then adjust downwards for gas boiler inefficiency and upwards or downwards depending on whether the homeowner keeps rooms cold or hot compared with MCS room temperatures. The MCS air change defaults are far too high, averaging 1.5 ACH (air changes per hour) whereas the average home at average wind speeds is typically 0.5 ACH, so the MCS by default overstates air permeability by a factor of 3. The MCS also has default U values which are far too high for many elements e.g. 2.1 for triple glazing whereas modern good quality triple glazing Uw's are typically 0.8 to 1.0. I spend a lot of time during the survey verifying fabric, trying to observe cavity wall depth and insulation, asking home owners when the insulation was installed, building reg certificates, invoices for new replacement windows etc. Generally using this more careful methodology my room by room heat losses are within 10% of the smart meter data. The MCS also doesn't account for internal heat gains: metabolic, appliances, hot water, solar etc., which is typically 0.4 to 1.0 kW which the heat pump won't need to produce. Where I have been asked to do heat loss calculations to check other installers calculations I see them typically 50% to 200% too high, worst case has been 400%. Often the root cause as suggested by the homeowner on the video is completely missing cavity wall insulation. The typical side effect of this is the heat pump short-cycles inefficiently, and that the weather compensation curves are typically set inefficiently too high. Generally oversizing the heat pump slightly is ok, some short-cycling appears not to reduce performance too much but getting weather compensation curves too high does reduce performance, but can be fixed post installation. Government research suggests that the average UK heat pump is 280% efficient, compared with Heat Geek installations which have more careful design which typically achieve 400%.
I'm slightly alarmed watching this video (which was a great discussion by the way) because I'm spending a lot of time and money upgrading fabric, radiators and airtightness to get ready for a heat pump as i renovate the house. But will any of that be counted by the MCS process?
I've done two heat loss calculations (MCS and heatpunk) and have established all the materials and therefore likely U value around my house. I've used these calculations to guide me on the best bang for the buck renovations to do. Real data (meter and smart home devices) validate the calculations.
Have i wasted my time if an installer is just going to stick to "out the box" MCS numbers?
I hired a company to do a full heat transfer measurement of our house, for all the components(walls, windows, roof…). I was surprised to find out that the heat transfer for the walls (Porotherm 25cm + 10cm EPS) was measured at U=0,45, instead of the “standards” of 0,27. Multiply this by the total area of the walls (210m2) and then multiply with the Delta T……you get the picture
Is there a workaround within the MCS system of oversizing? The default desired temp feel so high (22 degrees). Is this really a requirement in the UK. If not can it be reduced at the design stage? Impacting the heat loss as a result.
It seems the cusp is where the home is close to 14kw heat loss.. oversizing means 2 units and twice the cost…might as well leave the gas boiler just in case and forego the grant, and go with 1 unit. You are no worse off! Our house is 260 sq metres (very well insulated to 2016 building regs) - annual LPG usage suggests we need c. 9 kw. Heat loss calc suggests 15kw - 20kw .
Wall insulation question - can you not take the temp of the internal wall and the same spot on the external and have a calculation of the potential loss of heat?
Unfortunately, that's very inaccurate. The external surface temperature will be very dependant on wind speed and thermal radiation. An added complication is that cavity wall installs have often been fine badly with large voids, so the insulation can vary a lot from location to location. At the more extreme end, a friend of mine had all the cavity wall insulation guarantee paperwork when he bought his house but then found he had absolutely no cavity wall insulation actually installed. Presumably the "installer" pocketed the grant funding.
Heatloss of 100 W per sqm. Here it is normally around 20 in buildings from this century and up to 40 in older cottages. How do you actually build your houses, out of sticks?
Surely the biggest danger of using your gas usage to size a heat pump is that people use gas central heating very differently to a heat pump. For example, not many people with gas central heating will run their heating seven days a week, twenty four hours a day and have all their radiator valves fully open...
Can I please ask how do you guys factor in hot water demand and the effect it may have on the heating.For example we have just had a heat loss for a new build come back at 3,4kw but the client wants a 250ltr. Cylinder. Vaillant say the max size of cylinder a 3.5kw heat pump can heat is 200ltr because it would take too long for the 3.5 to heat 250 ltr from 10 degrees to 50 degrees
Our house is set to 22°c living room 24°c and even then my wife will feel cold. Our heatpump so far has worked well but I’m yet to have a full winter with it, so time will tell.
What do you think of the 'heating degree days' (HDD) method of predicting heat loss. From memory you download the HDD figure for your location, divide that figure into your total energy input (gas + electricity + solar PV in my case) and it comes up with estimate of heat pump sizing.
Reason for the question is that I downloaded an Excel model from the net, fed in my figures and was told that my 3 bed, 1990's detached house needed a pump size of 3.4 kW which seems way too low to me. As an example my gas boiler modulates down to 5 kW and the heating load is more than enough to keep it firing continuously during winter.
PSW - Would be grateful if someone could point me at alternative spreadsheets to experiment with.
11:00 or if you've sold the house & the new people are cold.
Guys, you said divide gas usage by 2000 while this guys says 2900: ruclips.net/video/hCeghKa3liM/видео.html (see 8 mins 7 secs for the final calculation and 6 mins 45 secs for the explanation). That's quite a difference and I was wondering why?
Fair question, and I don’t know why Michael is saying 2900, but I would take Graham’s number of 2,000 because he is one of the most experienced heating engineers out there.
@@RenewableHeatingHub Michael de Podesta is a well known and respected Physicist. It might be worth asking Graham to take a look at the video I linked as the calculation is explained in detail. Would be good to know why there is a difference?
@@darrenadams2640The number 2900 vs. 2000 is actually a variable 'heating degree days', which depends on location. It's discussed in detail later in that video, at around 17 minutes. HTH
Heating degree days, in Manchester the figure is 2380.
Using energy data isn’t the right way to go because as has been stated. What the current owner does could well be different to a new owner, for example I have my heating in twenty four seven others might not.
It shouldn't be used alone, but as the only empirical data to validate the heat loss calculations, it really can't be ignored either.
MCS ignores other heat sources from people, devices, solar gain, and cooking. It hugely overestimates ventilation losses. It relies on accurate fabric U value estimations.
Real data is real data - any installer who can't try to reconcile theoretical values to the real ones isn't worth working with IMHO.