Was the question about accounting for DHW temps ever answered? If the boiler is supplying temps lower than the DHW requirements, how is this accommodated?
Thank you for your question. Most combi-boilers or high efficiency boilers offer a DHW supply temperature limit and a space heating temperature limit. This allows you to set a space heating supply temperature and bypass and a higher supply water temperature to provide domestic water heating and quicker domestic water recovery times. This still allows you to maximize efficiency of the boiler using lower supply temperatures for space heating which will have longer run cycles. Higher temperatures for DHW heating will drop the efficiency slightly but this is needed to provide fast domestic water recovery and capacity keeping in mind the run time will be less for domestic water heating then space heating.
The heat load of the space is always changing as outdoor temperature changes. A modulating boiler will have longer run cycles at lower outputs to provide better efficiency and comfort. An oversized or single-stage boiler will tend to short cycle providing more cycles and lower efficiency. It is more important to consider the design building load, changing load, heat delivery system and system components to cover the changing loads, provide consistent run cycle and overall best system efficiency.
Sizing for the load is the first and most important step.
Thank you Hot Rod!
Was the question about accounting for DHW temps ever answered? If the boiler is supplying temps lower than the DHW requirements, how is this accommodated?
Thank you for your question.
Most combi-boilers or high efficiency boilers offer a DHW supply temperature limit and a space heating temperature limit. This allows you to set a space heating supply temperature and bypass and a higher supply water temperature to provide domestic water heating and quicker domestic water recovery times. This still allows you to maximize efficiency of the boiler using lower supply temperatures for space heating which will have longer run cycles. Higher temperatures for DHW heating will drop the efficiency slightly but this is needed to provide fast domestic water recovery and capacity keeping in mind the run time will be less for domestic water heating then space heating.
How many hours out of the day, and how my cycles in a day would you say is ideal for a boiler to operate?
The heat load of the space is always changing as outdoor temperature changes. A modulating boiler will have longer run cycles at lower outputs to provide better efficiency and comfort. An oversized or single-stage boiler will tend to short cycle providing more cycles and lower efficiency. It is more important to consider the design building load, changing load, heat delivery system and system components to cover the changing loads, provide consistent run cycle and overall best system efficiency.